fix: auto-deny permissions and emit events in non-interactive mode

[elithrar]

Fixes issues where permissions requests block indefinitely in CI/GitHub Actions, with no output indicating why. I keep running into this in CI runs, especially when the harness is trying to solve a problem or I'm testing/building plugins.

Since there's no way to prompt a user, it should just auto-deny by default + emit this to the logs so users can understand what happened.

Changes

• Add isInteractive() utility - checks CI env var, OPENCODE_CLIENT, and TTY state
• Auto-deny permission requests when !isInteractive() (no one to approve)
• Emit permission.asked events before denying so they're visible in logs
• Subscribe to permission events in github.ts and run.ts with actionable guidance on how to allow
• Add OPENCODE_EMIT_SUBAGENT_EVENTS flag for verbose subagent output in CI
• Add emit_subagent_events input to GitHub Action
• Deny question permission by default in GitHub Action sessions (merged from dev)

isInteractive() Logic

Only auto-denies for the CLI client in non-TTY/CI environments:

1. OPENCODE_FORCE_INTERACTIVE=true → interactive (for tests)
2. CI=true → non-interactive (auto-deny)
3. OPENCODE_CLIENT is not cli (e.g. desktop) → interactive (GUI handles permissions)
4. Otherwise, check stdin.isTTY && stdout.isTTY

current possible OPENCODE_CLIENT values: cli (default), desktop

Example Output

When a permission is denied in CI:

| Denied  external_directory: /tmp/opencode-source
  To allow, add to opencode.json: { "permission": { "external_directory": "allow" } }

Merge Conflict Resolution

Resolved conflict with dev branch - combined:

• Permission config from dev (deny question prompts in GitHub Action context)
• Event unsubscribe cleanup from this PR branch