fix(browse): remove the dead security shield + unfed /health.security (re-derived from #2557)

The sidebar's SEC shield has been dead UI since the PTY terminal rewrite:
nothing set its data-status, nothing unhid it, and the /health.security
field behind it read getStatus() off ~/.gstack/security/session-state.json
— a file whose ONLY writer (sidebar-agent.ts) was deleted with the chat
path. /health therefore reported a permanent 'inactive', or a stale
FALSE-GREEN 'protected' wherever an old state file survived on disk (a
single unit-test run was enough to plant one). A green shield sourced from
leftover state reads as "no threats detected" when the real state is "not
measured" — the same fail-open class as #2026.

Removed (dead surfaces only): the shield markup/CSS and the stale
sidepanel.js comment; the /health security field and server.ts's getStatus
import; getStatus / SecurityStatus / StatusDetail / SessionState /
read+writeSessionState (and security.ts's dead child_process import); the
session-state + getStatus unit tests — including the round-trip test that
wrote real fixture data into ~/.gstack and left /health green forever.
(The PR's security-sidepanel-dom.test.ts deletion already happened on main
via #2230; its resolveDisconnectCause guard landed via the #2085 typeof
fix. Neither re-applied.)

Kept, per ENG-OV9 — security.ts has LIVE consumers: the pure combiner
(combineVerdict + THRESHOLDS), canary utilities, and extractDomain stay;
server.ts's /pty-inject-scan L4 path (isSidecarAvailable + scanWithSidecar)
is untouched. browse/test/server-security-surface.test.ts pins BOTH
directions: the dead surface stays dead (no /health security field, no
getStatus import, no reader of the security session-state file, shield
markup gone) and the live half stays live (sidecar wiring in server.ts,
combiner/canary exports in security.ts, /health carries no token — the
v1.63 regression wall). A future re-feed from LIVE signals must update
that test deliberately rather than resurrect the state-file path.

F13 (same commit): CLAUDE.md's Sidebar security stack section, ARCHITECTURE.md's
prompt-injection Visibility + critical-constraint paragraphs, and
BROWSER.md's security section now describe the removed surfaces as history,
not live features.

Net -166 lines. Tests: server-security-surface + security +
security-adversarial(+fixes) + security-integration + server-auth 114 pass;
sidepanel-* + extension-token + extension-sender-auth 58 pass / 2 skip.

Re-derived from PR #2557 by @frederik-kaster-noygear.

Co-authored-by: Frederik Kaster <frederik.kaster@noygear.ai>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ARCHITECTURE.md

@@ -184,11 +184,11 @@ The Chrome sidebar agent has tools (Bash, Read, Glob, Grep, WebFetch) and reads
 
 5. **L6 ensemble combiner (`combineVerdict`).** BLOCK requires agreement from two ML classifiers at >= `WARN` (0.75), not a single confident hit. This is the Stack Overflow instruction-writing false-positive mitigation. On tool-output scans, single-layer high confidence BLOCKs directly — the content wasn't user-authored, so the FP concern doesn't apply.
 
-**Critical constraint:** `security-classifier.ts` runs only in the sidebar-agent process, never in the compiled browse binary. `@huggingface/transformers` v4 requires `onnxruntime-node`, which fails `dlopen` from Bun compile's temp extract directory. Only the pure-string pieces (canary inject/check, verdict combiner, attack log, status) are in `security.ts`, which is safe to import from `server.ts`.
+**Critical constraint:** `security-classifier.ts` runs only in the security sidecar subprocess (`security-sidecar-entry.ts`), never in the compiled browse binary. `@huggingface/transformers` v4 requires `onnxruntime-node`, which fails `dlopen` from Bun compile's temp extract directory. Only the pure-string pieces (canary inject/check, verdict combiner) are in `security.ts`, which is safe to import from `server.ts`. (The attack log lives in `tunnel-denial-log.ts`; the session-state/status surface was removed in #2557.)
 
 **Env knobs:** `GSTACK_SECURITY_OFF=1` is a real kill switch (skips ML scan, canary still injects). Model cache at `~/.gstack/models/testsavant-small/` (112MB, first run) and `~/.gstack/models/deberta-v3-injection/` (721MB, opt-in only). Attack log at `~/.gstack/security/attempts.jsonl` (salted sha256 + domain, rotates at 10MB, 5 generations). Per-device salt at `~/.gstack/security/device-salt` (0600), cached in-process to survive FS-unwritable environments.
 
-**Visibility.** The sidebar header shows a shield icon (green/amber/red) polled via `/sidebar-chat`. A centered banner appears on canary leak or BLOCK verdict with the exact layer scores. `bin/gstack-security-dashboard` aggregates local attempts; `supabase/functions/community-pulse` aggregates opt-in community telemetry across users.
+**Visibility.** A centered banner appears on canary leak or BLOCK verdict with the exact layer scores. `bin/gstack-security-dashboard` aggregates local attempts; `supabase/functions/community-pulse` aggregates opt-in community telemetry across users. (The sidebar header's SEC shield icon and the `/health` `security` field were removed in #2557: their only data source — `~/.gstack/security/session-state.json` — lost its only writer when the chat-path agent was ripped, so the shield reported stale or empty state. The live defenses report through their own call sites.)
 
 ## The ref system