docs(webview): record the lost-frame page as the third unauthenticated 200, and the inline-style limit

The lost-frame recovery page is answered ahead of the credential checks in both
auth hooks, which makes it the third unauthenticated 200 beside the two hook
routes, and the only one decided by request headers alone. CLAUDE.md's security
table listed exactly two, and docs/web-tabs.md is not where anyone auditing that
looks, so it now has a row in the table and a fourth property in
docs/security-architecture.md section 10b, including the `/` carve-out and its
credential-free condition. Both state the property that comes with it: a
non-browser client can set those headers, so an unauthenticated caller can tell a
registered route (401) from a non-route (200) and enumerate the route table,
accepted because the routes are public in docs/api-reference.md.

docs/web-tabs.md gains the landing-page case in layer 6 and a Known limits entry:
masking trades away the Referer safety net, only HTML is rewritten server-side,
and a root-absolute url() inside an inline <style> block has the masked document
as its Referer, so it 404s where the Referer fallback used to rescue it. External
stylesheets are unaffected.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

CLAUDE.md

@@ -364,6 +364,7 @@ Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. L
 | **Sessions**      | 24h cookie (`codeman_session`), auto-extend, device context audit                                                                                                                                           |
 | **Rate limit**    | 10 failed auth/IP → 429 (15min decay). QR and hook-secret have separate buckets, so neither can lock out login                                                                                              |
 | **Hook bypass**   | `/api/hook-event` + `/api/status-telemetry` skip Basic auth (localhost-only, schema-validated), but when auth is active the loopback bypass requires `X-Codeman-Hook-Secret` **unconditionally** (Codeman cannot detect a user's own loopback reverse proxy) |
+| **Lost-frame page** | The THIRD unauthenticated 200, beside the two hook routes, and the only one decided by request headers alone: a `GET`/`HEAD` carrying `Sec-Fetch-Dest: iframe\|frame`, `Accept: text/html` and mode `navigate` (or none), for a path that is NOT a registered route (never `/api/`, `/ws/`, `/q/`), is answered BEFORE the credential checks with the static web-tab recovery page (`lostWebviewFramePage`: no reflected input, `default-src 'none'` plus its own script hash, `no-store`). `/` is the one registered route also admitted, only when the request carries neither `codeman_session` nor `Authorization` (nothing in Codeman frames its own root; a sandboxed frame has neither), since the landing page masks to exactly `/` and its reload otherwise rendered Codeman inside the web tab. ⚠️ A non-browser client can set those headers, so an unauthenticated caller can tell a registered route (401) from a non-route (200) and enumerate the route table; accepted, the routes are public in `docs/api-reference.md`. Pinned by `test/webview-auth-exemption.test.ts` + `test/webview-lost-root-frame.test.ts` |
 | **Tunnel**        | Enabling a tunnel **refuses** without `CODEMAN_PASSWORD` unless exposure is acknowledged via `CODEMAN_ALLOW_UNAUTHENTICATED_NETWORK=1` or the per-request `acknowledgeUnauthTunnel:true` action field (never persisted) |
 | **Validation**    | Zod schemas, Unicode-aware path allowlist regex, env prefix allowlist (`CLAUDE_CODE_*`/`OPENCODE_*`/`CODEX_*`/`GEMINI_*`/`GOOGLE_*`/`ANTIGRAVITY_*`/`PI_*`/`GROK_*`/`XAI_*`/`DSH_*`/`DEEPSEEK_*`)                                                        |
 | **Headers**       | CORS localhost-only, CSP, X-Frame-Options, HSTS if HTTPS                                                                                                                                                     |