Update all instances of "whitelist" terminology to "allowlist" for more
inclusive language. This is a comprehensive update across the entire codebase.

Changes:
- Backend: Updated config models, API endpoints, and window manager methods
  - Renamed struct fields: Whitelisted -> Allowlisted
  - Renamed config keys: whitelist_patterns -> allowlist_patterns
  - Updated API endpoints: /api/applications/whitelist -> /api/applications/allowlist
  - Renamed methods: IsWindowWhitelisted -> IsWindowAllowlisted

- CLI: Renamed commands and updated all help text
  - Renamed command file: whitelist.go -> allowlist.go
  - Updated command: focusstreamer whitelist -> focusstreamer allowlist
  - Updated all flags and output messages

- Frontend: Updated React components and API calls
  - Updated prop names: onToggleWhitelist -> onToggleAllowlist
  - Updated CSS classes: .whitelisted -> .allowlisted
  - Updated all UI text and labels

- Documentation: Updated all markdown files (README, CLI, ARCHITECTURE, TESTING)

No functional changes - this is purely a terminology update for inclusivity.