fix(security): delete the dead ML layers — transcript classifier and DeBERTa ensemble

The L4b Haiku transcript classifier and the opt-in DeBERTa ensemble
(GSTACK_SECURITY_ENSEMBLE=deberta, a documented 721MB download) had ZERO
production callers since the chat-path agent that invoked them was ripped.
The only live ML path is scanPageContent (testsavant) inside the security
sidecar subprocess. Deleted by import graph:

- security-classifier.ts 614 -> 265 lines: HAIKU_MODEL, checkTranscript,
  shouldRunTranscriptCheck, loadDeberta, scanPageContentDeberta, ToolCallInput,
  all DEBERTA_* consts + load state. Header now states the live truth
  (imported only by security-sidecar-entry.ts). downloadFile kept, name
  intact — it is an enumerated egress sink (HF model download).
- security-bunnative.ts + test: a research skeleton self-described as 'NOT a
  production replacement', shipped into src/ with zero importers.
- security-bench-ensemble{,-live}.test.ts + the Haiku response fixture: a
  paid live-model benchmark for a layer that could not fire. The
  security-classifier-tdz test's only case exercised checkTranscript — gone.
- security.ts: layer-model header rewritten to the live architecture;
  StatusDetail.layers -> {testsavant, canary}; getStatus() no longer requires
  the impossible transcript==='ok' for 'protected' (old on-disk session state
  with a transcript key is tolerated on read, never re-emitted).
- security-sidecar-entry.ts needed zero changes: it serializes
  getClassifierStatus() verbatim and no consumer read .transcript (verified
  in sidecar-client + server.ts).
- BROWSER.md security section matches reality (ensemble knob gone, 112MB not
  22MB, sidecar hosting documented). combineVerdict/THRESHOLDS retained as
  the pure, tested combiner of record — comments now flag transcript/deberta
  votes as producer-less.

Net: 26 pass in security.test.ts incl. a NEW regression test for stale-
transcript disk tolerance; egress-receipt tripwire green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/skill-validation.test.ts

@@ -1872,10 +1872,9 @@ describe('no compiled binaries in git', () => {
     // repository size without blocking those fixtures from living in git.
     // Known-good fixtures are exempted from the warning to keep CI logs clean.
     const MAX_BYTES = 2 * 1024 * 1024;
-    const knownLargeFixtures = new Set([
-      // Deterministic replay fixture for BrowseSafe-Bench. The live bench is
-      // expensive; this file is intentionally committed so the gate is free.
-      'browse/test/fixtures/security-bench-haiku-responses.json',
+    const knownLargeFixtures = new Set<string>([
+      // Currently empty — add repo-relative paths of intentionally-committed
+      // large fixtures here with a reason.
     ]);
     const oversized = trackedFiles.flatMap((f: string) => {
       if (knownLargeFixtures.has(f)) return [];
@@ -1902,11 +1901,6 @@ describe('no compiled binaries in git', () => {
   });
 });
 
-// `sidebar agent (#584)` describe block was here. sidebar-agent.ts and
-// the entire chat-queue path were ripped in favor of the interactive
-// claude PTY (terminal-agent.ts); these assertions had no target file.
-// Terminal-pane invariants are covered by browse/test/sidebar-tabs.test.ts
-// and browse/test/terminal-agent.test.ts.
 
 // ─── Browser-skills validation ──────────────────────────────────
 //