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>

scripts/test-free-shards.ts

@@ -74,13 +74,6 @@ const WINDOWS_FRAGILE_PATTERNS: Array<{ pattern: RegExp; reason: string }> = [
   // BROWSE_HEADLESS_SKIP=1 to skip the browser launch but still need a working
   // server, which they don't get on Windows.
   { pattern: /BROWSE_HEADLESS_SKIP|spawn\(\[['"]bun['"],\s*['"]run['"]/, reason: 'spawns the browse server subprocess (Bun-driven path is Windows-broken)' },
-  // Tests that read browse/src/sidebar-agent.ts — deleted in v1.14.0.0
-  // sidebar refactor (replaced by sidepanel-terminal.js). 10 security tests
-  // still reference it and fail on import. They've been broken on every
-  // platform since v1.14, but Bun on macOS/Linux reports the failure as a
-  // module-load error (exit 0) while Bun on Windows treats it as a hard
-  // fail (exit 1). Tracked as a follow-up: update or delete these tests.
-  { pattern: /sidebar-agent\.ts/, reason: 'reads deleted browse/src/sidebar-agent.ts (pre-existing breakage from v1.14.0.0 sidebar refactor)' },
 ];
 
 // Explicit known-Windows-incompatible test files that don't fit a regex