feat: restore-all session recovery, ?file= deep links, offline PWA

Session recovery: more than one pending snapshot adds a 'Restore all'
button to the Recover Drawing modal — every snapshot goes through the
exact same guarded path as a single restore (deleted only after its
own open succeeds). The open-tab list and active tab persist to
localStorage on web (open/save/close) and the remembered tab is
re-selected once a restore batch settles; the modal notes how many
drawings the session had. Nothing is auto-opened.

Deep links: ?file=<url|name> opens a drawing at boot. http(s) URLs
must end in .dwg/.dxf and are fetched with the same streaming,
64 MB-capped, 8 s-deadline reader the remote images use, then go
through the guarded open queue; cross-origin opens announce the
origin first. Bare names resolve from the browser's recent storage,
with a hint when absent. Everything else (file:, javascript:, drive
letters, non-drawing tails) is refused with a console note.

Offline PWA: the app was installable (manifest) but downloaded its
55 MB bundle on every visit. A cache-first service worker now serves
the whole bundle from Cache Storage after one online visit —
navigations network-first so updates land, hashed assets
stale-while-revalidate, non-GET/cross-origin passthrough, old caches
cleaned on activate, and the waiting-worker update flow documented.
The build wrapper stamps the cache version from the bundle hash and
hard-fails if sw.js is missing or unstamped.

Also fixes a locale group mismatch on the DATALINK pick notice
(catalog said a display group that does not exist in the ftl
sources).

README.md

@@ -89,6 +89,8 @@ The project is under active development. Keep backups of important production dr
 
 Use the [web app](https://www.opencadstudio.com) for immediate access with no installation. Drawings are selected through the browser and saved as local downloads.
 
+The web app also accepts a `?file=` URL parameter, so a shared or embedded link can open a drawing directly: `?file=<url-encoded https://example.com/plan.dwg>` fetches and opens that drawing (only `http(s)` URLs ending in a `.dwg`/`.dxf` name), while `?file=plan.dwg` reopens a drawing previously opened in the same browser. Opening from another origin is announced on the command line before the fetch starts.
+
 Use the desktop application for native file associations, file-manager thumbnails, system printing, PDF output, external plugins, command scripts, and headless automation. Release builds are available for Windows, Linux, and Apple Silicon macOS.
 
 ## Install
@@ -181,6 +183,8 @@ never go missing from the bundle):
 sh scripts/build-web.sh
 ```
 
+The bundle ships a service worker (`web/sw.js`, deployed at `/app/sw.js`) that caches the app shell: after one online visit the app starts fully offline and the ~55 MB wasm bundle is served from the browser cache instead of re-downloaded. `build-web.sh` stamps a hash of the finished bundle into `sw.js` as the cache version, so every deploy ships a fresh cache and stale ones are cleaned up automatically.
+
 ## Automation
 
 The desktop binary supports one-shot conversion, a persistent headless server, and a client-neutral MCP endpoint for AI applications: