feat(cli): add doctor command for installation health checks (#334)

Implements a comprehensive 'doctor' command that diagnoses oh-my-opencode
installation health with a beautiful TUI output.

Checks performed:
- OpenCode installation (version, path, binary)
- Plugin registration in opencode.json
- Configuration file validity (oh-my-opencode.json)
- Auth providers (Anthropic, OpenAI, Google)
- Dependencies (ast-grep CLI/NAPI, comment-checker)
- LSP servers availability
- MCP servers (builtin and user)
- Version status and updates

Features:
- Beautiful TUI with symbols and colors
- --verbose flag for detailed output
- --json flag for machine-readable output
- --category flag for running specific checks
- Exit code 1 on failures for CI integration

Closes #333

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/cli/doctor/index.ts

@@ -0,0 +1,11 @@
+import type { DoctorOptions } from "./types"
+import { runDoctor } from "./runner"
+
+export async function doctor(options: DoctorOptions = {}): Promise<number> {
+  const result = await runDoctor(options)
+  return result.exitCode
+}
+
+export * from "./types"
+export { runDoctor } from "./runner"
+export { formatJsonOutput } from "./formatter"