feat(detector): deprecate --fast (now a no-op, full scan always)

Since the jsdom removal the static HTML/CSS analysis is fast (~4ms/file) and
covers every rule, so the regex-only `--fast` path only loses coverage (it
ran ~10 of 41 rules) for no real speed win. It's a foot-gun: a `--fast` scan
can read "clean" because most rules silently don't run.

Deprecate gracefully rather than hard-remove: the flag is still accepted (so
existing CI scripts don't break) but ignored, with a one-line stderr notice,
and the full scan always runs. Dropped from --help and the example. Removed
the `--fast` suggestion from the many-files warning and from critique.md's
scan guidance.

Ships to users via a CLI release (npm) and rides the next skill release in
the bundled detector. Tests updated to assert the deprecation behavior.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/detect-antipatterns.test.js

@@ -720,9 +720,10 @@ describe('CLI', () => {
     expect(JSON.parse(stdout.trim())).toEqual([]);
   });
 
-  test('--fast mode works', () => {
-    const { code } = run('--fast', path.join(FIXTURES, 'should-flag.html'));
-    expect(code).toBe(2);
+  test('--fast is accepted but deprecated (no-op, full scan still runs)', () => {
+    const { code, stderr } = run('--fast', path.join(FIXTURES, 'should-flag.html'));
+    expect(code).toBe(2); // still flags the planted anti-patterns via the full scan
+    expect(stderr).toContain('--fast is deprecated');
   });
 
   test('linked stylesheet detected (static HTML/CSS default)', () => {

tests/lib/detector-bundle.test.js

@@ -21,7 +21,7 @@ describe('skill detector bundle', () => {
   test('critique references the bundled detector command', () => {
     const critique = fs.readFileSync(path.join(ROOT, 'skill/reference/critique.md'), 'utf-8');
 
-    expect(critique).toContain('node {{scripts_path}}/detect.mjs --json [--fast] [target]');
+    expect(critique).toContain('node {{scripts_path}}/detect.mjs --json [target]');
     expect(critique).not.toContain('npx impeccable detect');
   });
 });