fix(security): delete dead exports the ripped chat path left behind

Three-way split by importer class:

(a) Zero importers, deleted: the whole attack-attempt logging cluster in
security.ts (logAttempt, AttemptRecord, salted hashPayload + device-salt,
attempts.jsonl rotation, telemetry spawn plumbing incl.
buildTelemetrySpawnCommand/resolveBashBinary — the LIVE attempts.jsonl writer
is tunnel-denial-log.ts with its own rotation); the decision-file handshake
(writeDecision/readDecision/clearDecision/excerptForReview — written for
sidebar-agent's poll loop, which no longer exists); sidebar-utils.ts (whole
module — its sanitizeExtensionUrl 'sanitized before embedding in a prompt'
for the deleted prompt builder); 8 dead server.ts imports (sanitizeExtensionUrl,
generateCanary, injectCanary, writeDecision, rotateRoot, serializeRegistry,
restoreRegistry, clearAgentRecord); buildPtyClearCookie + buildSseClearCookie;
WEBDRIVER_MASK_SCRIPT (orphaned by the D7 stealth narrowing — applyStealth
never used it).

(b) Dead-pin tests edited with their exports: the 'still exported' pin in
stealth-layer-c, the string-content describe in stealth-webdriver (its live
applyStealth behavioral coverage untouched), the clear-cookie assertions,
security-review-flow.test.ts deleted whole (all 4 describes exercised the
dead decision mechanism, incl. a 'simulated sidebar-agent poll loop').

(c) KEPT deliberately: leaseCount (live behavioral coverage),
extractPtyCookie + validatePtySessionToken (extractPtyCookie is adopted by
the terminal-agent cookie-parse unification later in this wave),
resetSessionMarker + clearContentFilters (test-support API for the live
content-security layer).

Also fixes two pre-existing red pins found while here, invisible until the
free suite got a CI job: the v1.44 spawnClaude->maybeSpawnPty rename in
terminal-agent.test.ts, and a cross-file test-isolation bug where
content-security.test.ts's clearContentFilters() wiped the auto-registered
url-blocklist filter for every later file in the same bun process
(security-integration.test.ts failed on co-run; afterAll now restores it).

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

browse/src/stealth.ts

@@ -461,14 +461,6 @@ export async function applyStealth(context: BrowserContext): Promise<void> {
   }
 }
 
-/**
- * The legacy single-line webdriver mask, exported for backwards
- * compatibility with any caller that uses it directly. New callers
- * should use applyStealth() which includes this plus the Layer C
- * additions.
- */
-export const WEBDRIVER_MASK_SCRIPT = `Object.defineProperty(navigator, 'webdriver', { get: () => false });`;
-
 /**
  * Args added to chromium.launch's `args` to suppress the
  * AutomationControlled blink feature. This is independent of the init