Closes the bandwidth-abuse vector on the in-app update flow. Both
endpoints now sit inside the authed.Group; APK additionally gets a
60s/user rate limit to suppress accidental hammering or scripted
abuse.
### Server
- internal/api/client_assets.go:
- clientAPKAllowDownload(): in-memory map[userID]time.Time under
a mutex. Returns 0 (allow) or wait duration (block).
- handleClientAPK reads user from context, checks the limit,
returns 429 + Retry-After header if blocked.
- testResetClientAPKRateLimit() lets tests start clean.
- internal/api/api.go: routes moved from the root /api group into
the authed.Group block (alongside /quarantine, /requests, etc.).
- Tests: added TestClientAPK_401WhenUnauthenticated and
TestClientAPK_RateLimit_429OnRapidSecondCall (also verifies
different user gets a fresh slot). Existing tests updated to use
authedRequest() helper.
### Web
- MobileAppDownload.svelte: switched from bare fetch (no credentials)
to api.get<>() which carries the session cookie. 404 / 401 /
network errors all silently hide the download row.
- Removed the login-page mount entirely — pre-auth surfaces should
never show this. Settings → Mobile app section keeps it for
logged-in users.
Flutter unaffected: dio's Bearer interceptor already attaches the
token, and the polling only fires once the post-login shell mounts
the banner widget.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen
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