Unknown --targets values silently discarded, --write becomes a misleading no-op

[royalpinto007]

Problem

run([dir, '--write', '--targets', 'bogus']) exits 0, writes nothing, and prints "Run with --write..." even though --write was passed: unknown targets are silently discarded.

Where

src/cli.js (targets filtered against TARGETS, unknowns dropped) + src/report.js (misleading hint).

Acceptance

Add a failing test first with --targets bogus, expecting exit 2 naming the valid targets. Then fix.

[mikemikimike]

Implemented in PR #12.

• Unknown --targets values now fail before scanning or writing, with exit code 2 and the supported target list (cursor, gemini, generic).
• Mixed input such as bogus,cursor is rejected atomically, so no ignore file is partially written.
• Added regression coverage, bumped the package to 0.1.3, and documented the fix in CHANGELOG.md.
• Local verification: npm test (9 passed), CLI JSON smoke test, and Node syntax checks.
• GitHub Actions CI passed: run 34026204018.

Valid target names and existing report behavior are unchanged.