feat(cli): extend run command with port, attach, session-id, on-complete, and json options

Implement all 5 CLI extension options for external orchestration:

- --port <port>: Start server on port, or attach if port occupied
- --attach <url>: Connect to existing opencode server
- --session-id <id>: Resume existing session instead of creating new
- --on-complete <command>: Execute shell command with env vars on completion
- --json: Output structured RunResult JSON to stdout

Refactor runner.ts into focused modules:
- agent-resolver.ts: Agent resolution logic
- server-connection.ts: Server connection management
- session-resolver.ts: Session create/resume with retry
- json-output.ts: Stdout redirect + JSON emission
- on-complete-hook.ts: Shell command execution with env vars

Fixes #1586

src/cli/run/index.ts

@@ -1,2 +1,7 @@
 export { run } from "./runner"
-export type { RunOptions, RunContext } from "./types"
+export { resolveRunAgent } from "./agent-resolver"
+export { createServerConnection } from "./server-connection"
+export { resolveSession } from "./session-resolver"
+export { createJsonOutputManager } from "./json-output"
+export { executeOnCompleteHook } from "./on-complete-hook"
+export type { RunOptions, RunContext, RunResult, ServerConnection } from "./types"