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>

CLAUDE.md

@@ -22,7 +22,7 @@ Cortex_and_Inara_dev/
     main.py              ← App entry point, router registration
     config.py            ← All settings (pydantic-settings, reads .env)
     persona.py           ← Two-level identity: user + persona, path resolution, ContextVars
-    llm_client.py        ← Claude CLI + Gemini CLI subprocess backends
+    llm_client.py        ← Claude CLI + Gemini CLI subprocess backends + Anthropic SDK direct
     orchestrator_engine.py ← Gemini API ReAct tool loop → Claude handoff
     context_loader.py    ← Builds system prompt from persona files (tier 1–4)
     session_store.py     ← In-memory + file session persistence
@@ -139,9 +139,10 @@ http://localhost:8000/docs
 - **Orchestrated tasks** go to `POST /orchestrate` — returns a job_id, result is polled
 
 ### LLM Backends
-- `llm_client.py` manages Claude CLI (`claude --print`) and Gemini CLI (`gemini -p`) subprocesses
+- `llm_client.py` manages Claude CLI (`claude --print`), Gemini CLI (`gemini -p`), and Anthropic SDK (`anthropic_api` type) subprocesses/calls
 - `orchestrator_engine.py` uses the Gemini **API** (google-genai SDK) — completely separate from the Gemini CLI
 - Claude OAuth token is read live from `~/.claude/.credentials.json` (never rely on stale env var)
+- `anthropic_api` backend: user-configured API key from `providers.anthropic.credentials` in `model_registry.json` — uses `anthropic.AsyncAnthropic`
 
 ### Tool Strategy
 - Orchestrator tools live in `cortex/tools/` — separate from the `ae_*` MCP tools