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/on-complete-hook.ts

@@ -0,0 +1,42 @@
+import pc from "picocolors"
+
+export async function executeOnCompleteHook(options: {
+  command: string
+  sessionId: string
+  exitCode: number
+  durationMs: number
+  messageCount: number
+}): Promise<void> {
+  const { command, sessionId, exitCode, durationMs, messageCount } = options
+
+  const trimmedCommand = command.trim()
+  if (!trimmedCommand) {
+    return
+  }
+
+  console.error(pc.dim(`Running on-complete hook: ${trimmedCommand}`))
+
+  try {
+    const proc = Bun.spawn(["sh", "-c", trimmedCommand], {
+      env: {
+        ...process.env,
+        SESSION_ID: sessionId,
+        EXIT_CODE: String(exitCode),
+        DURATION_MS: String(durationMs),
+        MESSAGE_COUNT: String(messageCount),
+      },
+      stdout: "inherit",
+      stderr: "inherit",
+    })
+
+    const hookExitCode = await proc.exited
+
+    if (hookExitCode !== 0) {
+      console.error(
+        pc.yellow(`Warning: on-complete hook exited with code ${hookExitCode}`)
+      )
+    }
+  } catch (error) {
+    console.error(pc.yellow(`Warning: Failed to execute on-complete hook: ${error instanceof Error ? error.message : String(error)}`))
+  }
+}