fix: isolate development icon catalog

[rdlabo]

Summary

• use Angular's official isDevMode() for development-only catalog registration
• ship the complete Ionicons catalog as an isolated lazy artifact so production startup does not download it
• preserve the documented Angular 18–22 peer range and document the migration behavior

Verification

• npm test — 92 tests passed
• npm run lint
• npm run build
• packed tarball verified with Angular 18.2 clean consumer
• Seatkeep optimized build: catalog isolated as an 816.65 kB lazy chunk with zero catalog bytes in the initial graph
• manager review: approved
• independent acceptance review: accepted

The package version and README are intentionally unchanged; maintainers will choose the release version separately.