fix: macOS dictation mic permission prompt on main thread

[Dimillian]

Motivation

• The microphone permission dialog on macOS could fail to appear because the permission request was not dispatched on the main thread, causing dictation startup to proceed without showing the system prompt.

Description

• Plumb an AppHandle into request_microphone_permission and ensure trigger_microphone_permission_request() is invoked via run_on_main_thread so the system dialog appears reliably on macOS in src-tauri/src/dictation.rs.
• Wire the app handle through the dictation_start call site and update the non-macOS stub to accept the same signature for parity.
• Use a oneshot channel to propagate errors from the main-thread call back to the async permission flow and surface failures appropriately.

Testing

• Ran npm run lint with no lint errors reported (passed).
• Ran npm run typecheck (tsc --noEmit) with no type errors reported (passed).

---

Codex Task

[Dimillian]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".