feat(language): implement timeout handling in initLanguage to prevent splash screen stalling

[MrDirkelz]

No description provided.

[johan-bell]

The approach is sound — bounding the never-settling boot promises with a static splash and live watchers means a timed-out boot still lands in a usable, self-healing state. A few blockers before this can go in:

• shared/src/db/database.ts:915 — the 10s DB_OPEN_TIMEOUT_MS wraps db.open(), which also runs Dexie version upgrades; a bumped index string re-indexes the whole docs table (incl. the multi-entry *fts index), so a full-corpus client on a slow device can exceed 10s and hard-fail into the error splash, where Reload just restarts the upgrade. Bound only the blocked/no-answer case (the blocked handler at :906 already detects it).
• app/src/main.ts:43 — the 45s watchdog only shows visible UI before app.mount(); after mount the static splash is gone and App.vue's loading splash has no error state, so a post-mount stall is still an endless spinner.
• app/src/globalConfig.ts:274 — the new LANGUAGE_BOOT_TIMEOUT_MS block landed between initLanguage's JSDoc and the function, so the doc now documents the constant.
• Comment style: several added comments narrate the bug/previous behaviour at multi-sentence length (database.ts:912, globalConfig.ts:278, main.ts:36, and the spec file headers) — that context belongs in the PR description, which is currently empty.
• Tests: initLanguage.spec.ts tests globalConfig (existing initLanguage tests live in globalConfig.spec.ts) and burns the real 5s timeout twice — fake timers would keep the suite fast.

[johan-bell]

Follow-up after a deeper hands-on pass: the two blockers in my review stand, with one softening on the first — the 10s timeout rejects the boot promise but does not abort the underlying Dexie open, so a legitimate schema upgrade continues in the background and a later reload can succeed. The user still lands on the error splash mid-upgrade though, so bounding only the blocked/no-answer case remains the ask.

Also flagging: #1974 introduces a static boot splash for the same window (in index.html, outside #app, removed after full startup). Both PRs can't merge as-is — worth converging with Chris on one implementation. This PR's error/reload panel, nosplash and prefers-reduced-motion handling plus #1974's placement (it covers the post-mount initLanguage window too, which would also close my second blocker about the watchdog having no visible UI after mount) would combine into the complete fix.