docs: align architecture and user guides with the current code

[setkyar]

What

Audit of docs/ and user-docs/en/ against the current code, fixing claims that no longer match and content that was missing. Docs + translation tooling only — no app code changes.

Architecture (docs/)

• /login never existed. docs/architecture/{frontend,system-overview,backend}.md and docs/dev/templates-vs-web.md listed a LoginPage.svelte SPA route. Auth is the Go-rendered token prompt (internal/ui/auth_page.go + embedded/auth.html), served by the auth middleware before the SPA loads. Replaced with the real behavior and documented NotFoundPage.
• /schedules was missing from the system-overview route table and the App.svelte route tree; added alongside the /api/schedules family and /api/chat/queue.
• SQLite schema drifted. backend.md said "six tables"; there are eleven (schedules, schedule_runs, review_comments, chat_queue_items, chat_queue_state were missing), plus the same omission in the system-overview DB row and directory layout.
• CSS routes are gone. pwa.go only serves manifest/service worker/icons/cat.webm; theme.css, index.css, menu.css, palette.css are no longer standalone routes — they are inlined in the SPA shell (plus schedules.css/settings.css, which were missing from the lists).
• Package layout: added internal/chatqueue/, internal/server/chat_queue.go, chat_queue_drainer.go, and request.go; synced the Server and workers.Manager struct snapshots with the code.
• Numbers/behavior: running-status recent-activity window is 800 ms, not 3 s; POST /api/chat returns 202 {"ok":true,"status":"queued"}, not "accepted"; Tailscale Serve only runs with PI_WEB_TOKEN set; server startup also starts the schedule loop + queue drainer (skipped in dev mode); mention-autocomplete helpers actually live under components/session/chat/; custom themes are picked in Settings → Appearance (the old header theme toggle is gone).
• Append-only claim: rename is not the only metadata append — auto-title (session_info) and entry labels (label) append too.
• Added the design-system and metrics docs to docs/README.md.

User guides (user-docs/en/)

• Roadmap: steering/queue (Steering/queue support in chat composer #46), scheduler (Scheduler: admin-gated scheduled prompts with triggers #44), configurable display defaults (Configurable defaults for Thinking, Tools, and Tool Output visibility #48), and git diff (part of File Explorer and Git Diff viewer (opt-in) #47) have shipped — moved them out of Next up/Planned.
• Keyboard shortcuts: documented ⌘/ / Ctrl+/ (shortcuts modal) and ⌘, / Ctrl+, (settings).
• llm-debug.md: pi-web status is not a binary subcommand; the actual command is /pi-web status (and /pi-web path) from inside pi.
• install.md: ?token= sets a pi_token cookie and redirects to the token-stripped URL, so the token does not linger in the address bar or history.

Translations

• Regenerated all 13 non-English locales (es fr de zh ja id ms vi th fil my km lo):
  • the four guides this PR changed — install, keyboard-shortcuts, llm-debug, roadmap
  • plus README and personal-assistant, which still predated the skills / pi-web-ctl additions from feat(skills): add schedule, notes, and settings skills #117
• scripts/build_userdocs.py now supports a --docs filter so only changed guides are translated:
  • build_userdocs.py --docs install roadmap — selected docs, all languages
  • build_userdocs.py es ja --docs install — both filters
  • A full run (no --docs) still translates every doc plus hero.json.
• Cost control: 78 paid pi calls for a full resync (52 for this PR's guides + 26 for the feat(skills): add schedule, notes, and settings skills #117 drift) instead of 104 — why and hero.json were untouched and skipped by the filter.

Verification

• python3 scripts/build_site.py assembles the VitePress source for all 14 locales from the edited English docs + regenerated translations.
• Structural check on all 52 translated files: code-fence count, table rows, headings, and URLs all match the English source.
• Relative-link check across all changed docs and translations: no broken links.
• Spot-checked that every locale contains the new content (/pi-web status, ⌘/, ?token=, shipped-roadmap entries).