Cleanup: break up the massive app.py into separate modules of manageable size.

docs/backend.md

@@ -4,13 +4,21 @@ The Python backend lives in `pagerite/`.
 
 ## `app.py`
 
-The FastAPI app. FastAPI's built-in API docs are disabled (`docs_url`/`redoc_url`/`openapi_url=None`) because `/docs` belongs to our content. Our own routes (content pages, `/_api/...`, `/_f/...`) are registered BEFORE `frontend.route(app, "/")` is called: fastapi-vue inserts its file routes at the position where `route()` was called (during `load()` in the lifespan), so anything defined earlier wins. The one exception is the content catch-all `/{path:path}`, registered AFTER `frontend.route()` so that built frontend assets still take priority over content slugs. The `Frontend` is constructed with `spa=False` explicitly: it only serves the built files without a catch-all.
+Thin FastAPI assembly: lifespan (open the kanta database, load the file store, the frontend build and GeoIP), the `FastAPI(...)` instance with built-in API docs disabled (`docs_url`/`redoc_url`/`openapi_url=None`) because `/docs` belongs to our content, the `server` header middleware, and router includes. The routes themselves live in specialized modules:
+
+- `state.py` — shared core, no routes: the environment-derived site constants (`HOSTNAME`, `SITE_URL`, `DB_PATH`, `FILES_DIR`, image/favicon tunables), the `data` root and its `kanta` handle (`Kanta(..., migrations="pagerite.migrations")`), the `analytics_store`, the fastapi-vue `frontend`, the page render cache and `_html_response`, the translator `dispatcher`, the slug charset helpers, and the `@kanta.bootstrap` hooks (demo seed, translator defaults).
+- `files.py` — the `FileStore` and image derivative helpers, and the file routes: `/_api/files`, `/_f/`, `/_themes/`, `/_fonts/`, the favicon settings endpoints.
+- `api.py` — the editor REST API and WebSockets: `/_api/pages`, `/_api/structure`, `/_api/settings`, `/_api/toggle-task`, `/_api/translations`, `/_api/ws/editor`, and the translator channel `/_translate/{clientkey}`.
+- `tracking.py` — visit analytics: GeoIP, client enrichment, favicon fetching, debounced broadcasts, the `/_ws` activity socket, the admin stream `/_api/ws/analytics`, and the `/_a` viewer page.
+- `pages.py` — the public content pages: `/`, `/sitemap.xml`, `/robots.txt` and the `/{path:path}` catch-all.
+
+Route ordering is load-bearing and lives in `app.py`: the api/tracking/files routers are included BEFORE `frontend.route(app, "/")` is called — fastapi-vue inserts its file routes at the position where `route()` was called (during `load()` in the lifespan), so anything registered earlier wins. The content catch-all `/{path:path}` is included AFTER `frontend.route()` so that built frontend assets still take priority over content slugs. The `Frontend` is constructed with `spa=False` explicitly: it only serves the built files without a catch-all.
 
 The build mirrors the URL space — hashed immutable assets under `/_assets/`, `favicon.ico` at the site root — and an `index.html` in the build would become a `/` route, so leave it out of the build to keep `/` ours.
 
-Generated HTML pages (content pages, category/404 placeholders, `/_a`) go through `_html_response`: zstd-compressed per request at level 9 when the client sends `accept-encoding: zstd` (no gzip fallback; static assets are pre-compressed by the `Frontend`), with `vary: accept-encoding` set and the ETag kept identical across encodings so `if-none-match` revalidation still works. In production the rendered bodies are cached in an LRU keyed by everything the output depends on — page kind, path, the site origin (social meta), encoding — and cleared wholesale by `_invalidate_pages()` on every content/settings change, which also bumps the in-memory render generation. The cache is bypassed in dev, where theme/design CSS is re-read from disk per request. Content pages carry an ETag built from the node's modified timestamp and the render generation; `/_a` instead gets a blake3 hash of the rendered body (it has no Node), with matching `if-none-match` revalidations answered by a 304.
+Generated HTML pages (content pages, category/404 placeholders, `/_a`) go through `state.py`'s `_html_response`: zstd-compressed per request at level 9 when the client sends `accept-encoding: zstd` (no gzip fallback; static assets are pre-compressed by the `Frontend`), with `vary: accept-encoding` set and the ETag kept identical across encodings so `if-none-match` revalidation still works. In production the rendered bodies are cached in an LRU keyed by everything the output depends on — page kind, path, the site origin (social meta), encoding — and cleared wholesale by `_invalidate_pages()` on every content/settings change, which also bumps the in-memory render generation. The cache is bypassed in dev, where theme/design CSS is re-read from disk per request. Content pages carry an ETag built from the node's modified timestamp and the render generation; `/_a` instead gets a blake3 hash of the rendered body (it has no Node), with matching `if-none-match` revalidations answered by a 304.
 
-Uploaded files, seed assets and fetched external-site favicons live in the `FileStore`: content-addressed files on disk under `<hostname>/files/` (`PAGERITE_FILES`), fully cached in RAM at startup — both the raw body and a zstd-compressed copy (kept only when smaller). `GET /_f/{name}` serves from the RAM cache with immutable caching, answering the zstd variant when the client accepts it; the name is the ETag. Uploaded raster images (and rasterized SVGs) are stored as `<hash>.orig<ext>` (internal only, never served) plus AVIF, WebP and JPEG derivatives, and pages link the extension-less `/_f/{hash}`: the server serves a format only when the Accept header lists it explicitly (`image/avif` → AVIF, `image/webp` → WebP, otherwise — including `*/*` — JPEG), with `vary: accept`; an explicit extension pins the format. `migrate_v2` rewrites old `/_f/{hash}.avif` article links to the bare form, backfills missing derivatives on disk, and drops the obsolete `version` field. Legacy databases that still carry blobs in a `files` kanta field or a flat `pages` store are migrated by `pagerite/migrations.py::migrate_v1` (kanta's `migrate_vN` mechanism, wired via `Kanta(..., migrations="pagerite.migrations")`), which rewrites the raw state before struct decoding — all schema/storage upgrades live in that module, none in the app lifespan.
+Uploaded files, seed assets and fetched external-site favicons live in the `FileStore` (in `files.py`): content-addressed files on disk under `<hostname>/files/` (`PAGERITE_FILES`), fully cached in RAM at startup — both the raw body and a zstd-compressed copy (kept only when smaller). `GET /_f/{name}` serves from the RAM cache with immutable caching, answering the zstd variant when the client accepts it; the name is the ETag. Uploaded raster images (and rasterized SVGs) are stored as `<hash>.orig<ext>` (internal only, never served) plus AVIF, WebP and JPEG derivatives, and pages link the extension-less `/_f/{hash}`: the server serves a format only when the Accept header lists it explicitly (`image/avif` → AVIF, `image/webp` → WebP, otherwise — including `*/*` — JPEG), with `vary: accept`; an explicit extension pins the format. `migrate_v2` rewrites old `/_f/{hash}.avif` article links to the bare form, backfills missing derivatives on disk, and drops the obsolete `version` field. Legacy databases that still carry blobs in a `files` kanta field or a flat `pages` store are migrated by `pagerite/migrations.py::migrate_v1` (kanta's `migrate_vN` mechanism, wired via `Kanta(..., migrations="pagerite.migrations")`), which rewrites the raw state before struct decoding — all schema/storage upgrades live in that module, none in the app lifespan.
 
 ## `data.py`
 
@@ -34,4 +42,4 @@ Any page with published children — a category page — lists them as a card gr
 
 ## `seed.py`
 
-Demo content written only when the database is first created, via a `@kanta.bootstrap` handler in `app.py`.
+Demo content written only when the database is first created, via a `@kanta.bootstrap` handler in `state.py`.