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/checks/index.ts

@@ -0,0 +1,31 @@
+import type { CheckDefinition } from "../types"
+import { getOpenCodeCheckDefinition } from "./opencode"
+import { getPluginCheckDefinition } from "./plugin"
+import { getConfigCheckDefinition } from "./config"
+import { getAuthCheckDefinitions } from "./auth"
+import { getDependencyCheckDefinitions } from "./dependencies"
+import { getLspCheckDefinition } from "./lsp"
+import { getMcpCheckDefinitions } from "./mcp"
+import { getVersionCheckDefinition } from "./version"
+
+export * from "./opencode"
+export * from "./plugin"
+export * from "./config"
+export * from "./auth"
+export * from "./dependencies"
+export * from "./lsp"
+export * from "./mcp"
+export * from "./version"
+
+export function getAllCheckDefinitions(): CheckDefinition[] {
+  return [
+    getOpenCodeCheckDefinition(),
+    getPluginCheckDefinition(),
+    getConfigCheckDefinition(),
+    ...getAuthCheckDefinitions(),
+    ...getDependencyCheckDefinitions(),
+    getLspCheckDefinition(),
+    ...getMcpCheckDefinitions(),
+    getVersionCheckDefinition(),
+  ]
+}