Add programmatic mixed-model Claude Desktop setup

[theFong]

Summary

• add an opt-in --desktop path to claude-code-setup.sh
• create and apply the separate Claude Desktop Gateway/3P profile without UI automation
• merge Anthropic's live model catalog with Desktop-safe Webster aliases in one picker
• support either a private ANTHROPIC_API_KEY or opt-in --anthropic-oauth reuse from macOS Keychain
• refresh and persist rotated Claude Code OAuth credentials without copying tokens into proxy config
• preserve Claude Code credential pass-through and isolate Anthropic, Webster, and Desktop sentinel credentials
• preserve unrelated Desktop configuration, create first-change backups, and relaunch into 3P mode

Validation

• bash -n install.sh claude-code-setup.sh test.sh
• node --test claude-code-model-proxy/test/proxy.test.mjs (21 tests)
• bash test.sh
• actionlint .github/workflows/bootstrap.yml
• git diff --check
• real macOS --desktop --anthropic-oauth install
• byte-idempotent second real install
• read-only --desktop --anthropic-oauth --check
• Claude Desktop logs: Gateway/3P active, 14 discovered models, picker 14, config health healthy
• live Webster route returned HTTP 200
• live Anthropic OAuth route was accepted by Anthropic and returned the account's current HTTP 429 usage-limit response (not an authentication error)