[judy] feat(pwa): installable PWA shell (manifest + service worker)

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Thread: th_19e6e6a8a5a_2979da (将 OpenForge 封装成可独立运行的 app)

What

Phase 1 of the "OpenForge as a Mac app" plan: make the existing web UI installable as a standalone Dock app via Chrome/Edge's "Install app" affordance. No native bundle, no Electron, no code signing — backend keeps running under launchd unchanged.

Changes

• web/manifest.webmanifest — name/short_name/icons (reuses existing branding/logo-forge-f-{32,48,256}.png), display: standalone + window-controls-overlay fallback, theme #0a0a0a to match the new Slack-ish palette.
• web/sw.js — minimal service worker. Stale-while-revalidate on a small allow-list of shell assets (style.css, app.js, /branding/, /assets/, manifest). All /api/* requests are network-only (belt + suspenders). CACHE_VERSION constant for easy bumps.
• server.py — whitelisted routes for /manifest.webmanifest and /sw.js. The SW response also sets Service-Worker-Allowed: / so its scope is unambiguous.
• web/index.html — <link rel=manifest>, theme-color, apple-mobile-web-app-* metas, and a deferred navigator.serviceWorker.register('/sw.js', { scope: '/' }). Registration failure is non-fatal.

Verification

Ran the server on a side port and curled:

$ curl -sD- -o/dev/null /manifest.webmanifest
HTTP/1.0 200 OK
Content-Type: application/manifest+json; charset=utf-8

$ curl -sD- -o/dev/null /sw.js
HTTP/1.0 200 OK
Content-Type: application/javascript; charset=utf-8
Service-Worker-Allowed: /

To install: open http://127.0.0.1:7878/ in Chrome → address bar shows an "Install app" icon → click → standalone window with Forge icon in Dock and Cmd-Tab.

Out of scope (deliberate)

• Tray / menu-bar icon, global hotkeys, native notifications → would need Tauri wrapper. Phase 2 if standalone window mode turns out not to be enough.
• PyInstaller-embedded backend → loses launchd auto-restart and forge update. Not worth it while OpenForge is single-user.

cc @scott

[github-actions]

🤖 bot-review (comment-only · phase 1)

Diff: 4 files changed, 170 insertions(+) @ f86a9e3

Red-line checks:

• ✅ A-7.5: no new 'forbidden' code in xiaof

Needs human review — these paths are not eligible for future auto-approve:

• server.py (HTTP routes / handler — never auto-approve)

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Phase 1: this bot leaves comments only. Auto-approve will be enabled per-path after 1–2 weeks of clean runs. Promotion plan: judy PR #42 follow-up.