feat: Anthropic SDK backend — API key alternative to Claude CLI OAuth

Adds `anthropic_api` model type so users can authenticate with a direct
Anthropic API key instead of (or alongside) the CLI OAuth session.

- model_registry.py: `anthropic_api` type; `save/get/remove_anthropic_api_key()`
  mirroring the Google account pattern; `save_cloud_model()` now picks type
  based on credential type (cli → claude_cli, api_key → anthropic_api);
  `_resolve_model()` merges api_key from the credential entry
- llm_client.py: `_anthropic_api()` backend (AsyncAnthropic SDK); dispatch
  and fallback wiring; usage tracking
- routers/local_llm.py: Anthropic API key management routes
  (POST /settings/local/anthropic-key, /anthropic-key/{id}/remove);
  `anthropic_api` badge and edit-form credential selector
- static/local_llm.html: Anthropic Cloud Provider block now shows API key
  management (add/remove); Add Model → Anthropic tab has credential selector
  (CLI vs API key)
- requirements.txt: enable anthropic>=0.40.0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

documentation/MASTER.md

@@ -43,7 +43,7 @@ Cortex is a self-hosted personal AI platform. It routes messages from any input
 | Distill safety | ✅ Live | Per-persona asyncio lock, per-endpoint cooldowns, Rebuild option |
 | Guided onboarding | ✅ Live | Setup Step 3 for OpenRouter; existing-user banner; settings quick-link |
 
-**65 orchestrator tools** across 17 domain modules — added 2026-05-12: `file_diff`, `git_status` / `git_log` / `git_diff` (read-only git inspection), `ae_db_query` / `ae_db_describe` / `ae_db_show_view` (SELECT-only Aether MariaDB access, admin, per-user credentials). `/settings/integrations` page added (admin-only). File attachments in chat (images for vision-capable local models; text/code files for all backends). Settings pages unified under `pg.css`. Added 2026-05-13: `task` cron type (full orchestrator loop on a schedule); monthly/yearly schedule formats (`monthly`, `monthly:DD:HH:MM`, `yearly:MM:DD:HH:MM`); Schedules web UI at `/settings/crons` (list, add, edit, pause, delete); HA inbound webhook tools toggle (orchestrator vs. direct LLM).
+**65 orchestrator tools** across 17 domain modules — added 2026-05-12: `file_diff`, `git_status` / `git_log` / `git_diff` (read-only git inspection), `ae_db_query` / `ae_db_describe` / `ae_db_show_view` (SELECT-only Aether MariaDB access, admin, per-user credentials). `/settings/integrations` page added (admin-only). File attachments in chat (images for vision-capable local models; text/code files for all backends). Settings pages unified under `pg.css`. Added 2026-05-13: `task` cron type (full orchestrator loop on a schedule); monthly/yearly schedule formats (`monthly`, `monthly:DD:HH:MM`, `yearly:MM:DD:HH:MM`); Schedules web UI at `/settings/crons` (list, add, edit, pause, delete); HA inbound webhook tools toggle (orchestrator vs. direct LLM); Anthropic API key backend (`anthropic_api` model type via Anthropic SDK — alternative to CLI OAuth).
 
 **Active users / personas:** scott/inara, holly/tina, brian/wintermute