fix: address commander-fork audit findings with critical bug fixes and tests

Fixed 5 critical bugs identified in comprehensive audit:
- version() event name extraction now handles short-only, long-only, and combined flags using attributeName()
- help event emission now fires both dynamic flag event AND stable 'help' event for compatibility
- EventEmitter.call(this) added to Command constructor for proper inheritance
- Option.negate detection tightened from indexOf to regex /(^|[\s,|])--no-/
- Option.name() now strips both -- and - prefixes for short-only flags

Added 5 comprehensive test files (24 tests total):
- test.version.short-only.spec.ts (3 tests)
- test.help.override.spec.ts (4 tests)
- test.unknown.attached.spec.ts (9 tests)
- test.eventemitter.early.spec.ts (4 tests)
- test.opts.custom-version.spec.ts (5 tests)

Updated documentation to accurately reflect fork as deliberately reduced subset:
- README.md: Added warning banner, compatibility matrix, supported API surface
- Removed FORK_NOTICE.md and FORK_PLAN.md (consolidated into README)
- README now clearly states "NOT a drop-in replacement"

All 199 tests passing.

Author: JohannesHoppe