fix(test): exorcise the sidebar-agent ghost from the test suite

browse/src/sidebar-agent.ts was deleted in the v1.14 sidebar refactor, but the
test suite kept testing it for 48 versions. Nothing noticed because the free
suite runs in no CI job and Bun-era module-load errors were suppressed in the
Windows shard runner via an exclusion pattern whose own comment documented the
breakage ('broken on every platform since v1.14 ... exit 0').

- Delete sidebar-security.test.ts + security-source-contracts.test.ts: crashed
  at module load (unguarded readFileSync of the deleted file); per-assertion
  triage confirmed every SERVER_SRC pin targeted the deleted chat prompt
  builder (zero hits in today's server.ts) — nothing to port.
- Delete sidebar-integration.test.ts: 11 of 13 tests exercised deleted
  endpoints (/sidebar-command queue, /sidebar-agent/event, chat buffer); the 2
  passing tests pinned only the blanket auth gate, covered by
  server-auth.test.ts + dual-listener.test.ts.
- Delete test/skill-e2e-sidebar.test.ts: E2E for the deleted queue flow.
- sidebar-ux.test.ts 1,669 -> 830 lines: 20 dead-chat describes + 15 dead
  tests removed (incl. 10 vacuous passes asserting on empty indexOf slices);
  2 stale pins on LIVE features fixed (content.js typed-catch CSSOM fallback,
  arrow-hint window widened). 95 pass / 0 fail.
- sidebar-tabs.test.ts: both failures were stale pins, not regressions —
  forceRestart's deliberate ws.close(4001) and the terminal-agent spawn that
  moved into spawnTerminalAgent() (identity-based kill refactor). 28 pass.
- touchfiles.ts: drop the three sidebar E2E entries from BOTH maps
  (E2E_TOUCHFILES + E2E_TIERS) — they pointed diff-selection at the deleted
  file, so those tests were unreachable by any diff.
- test-free-shards.ts: remove the now-dead sidebar-agent exclusion pattern.

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

test/helpers/touchfiles.ts

@@ -327,11 +327,6 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   'benchmark-workflow':            ['benchmark/**', 'browse/src/**'],
   'setup-deploy-workflow':         ['setup-deploy/**', 'scripts/gen-skill-docs.ts'],
 
-  // Sidebar agent
-  'sidebar-navigate':              ['browse/src/server.ts', 'browse/src/sidebar-agent.ts', 'browse/src/sidebar-utils.ts', 'extension/**'],
-  'sidebar-url-accuracy':          ['browse/src/server.ts', 'browse/src/sidebar-agent.ts', 'browse/src/sidebar-utils.ts', 'extension/background.js'],
-  'sidebar-css-interaction':       ['browse/src/server.ts', 'browse/src/sidebar-agent.ts', 'browse/src/write-commands.ts', 'browse/src/read-commands.ts', 'browse/src/cdp-inspector.ts', 'extension/**'],
-
   // Autoplan
   'autoplan-core':  ['autoplan/**', 'plan-ceo-review/**', 'plan-eng-review/**', 'plan-design-review/**'],
   'autoplan-dual-voice': ['autoplan/**', 'codex/**', 'bin/gstack-codex-probe', 'scripts/resolvers/review.ts', 'scripts/resolvers/design.ts'],
@@ -711,11 +706,6 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'benchmark-workflow': 'gate',
   'setup-deploy-workflow': 'gate',
 
-  // Sidebar agent
-  'sidebar-navigate': 'periodic',
-  'sidebar-url-accuracy': 'periodic',
-  'sidebar-css-interaction': 'periodic',
-
   // Autoplan — periodic (not yet implemented)
   'autoplan-core': 'periodic',
   'autoplan-dual-voice': 'periodic',