Add Apple Intelligence gRPC server

Implements a Swift gRPC server that exposes Apple's Foundation Models
(Apple Intelligence) over the network for LAN access.

Features:
- Complete: Unary RPC for prompt/response
- StreamComplete: Server streaming RPC for token-by-token responses
- Health: Check model availability
- Optional API key authentication via gRPC metadata
- Configurable host/port via CLI args or environment variables

Requires macOS 26 (Tahoe) with Apple Intelligence enabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

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+.build/
+.swiftpm/
+*.xcodeproj/
+xcuserdata/
+DerivedData/
+.DS_Store