feat: show T3 thread titles in Codex notifications

[obviousbread]

Closes #61.

What this does

Adds optional, read-only T3 Code context resolution for Codex completion notifications.

When a Codex notify payload contains a thread-id, Code-Notify checks whether that Codex thread is associated with a local T3 Code thread. If it is, the T3 thread title is used as the notification context instead of the workspace basename.

Before: Task Complete - WORK
After:  Task Complete - Investigate missing desktop notifications

Standalone Codex behavior is unchanged.

How it works

T3 Code stores its local state in ~/.t3/userdata/state.sqlite. The resolver:

1. Extracts thread-id from the existing Codex notify payload.
2. Opens the T3 database read-only.
3. Finds a Codex runtime whose resume_cursor_json.threadId matches the payload.
4. Resolves the associated title from projection_threads.
5. Returns the title only when it is a non-empty string.

Missing files, database locks, incompatible schemas, malformed JSON, unavailable Python, and unmatched threads all fall back to the existing workspace-name resolution.

Design decisions

• Best-effort: notification delivery never depends on the T3 lookup succeeding.
• Read-only: Code-Notify does not modify T3 state.
• Exact matching: the resolver uses the Codex thread ID instead of guessing from the most recently updated T3 thread.
• No new dependency: it reuses Python's standard sqlite3 module, which Code-Notify already uses for Codex state inspection.
• No new provider: T3 Code is optional context for Codex, not a separate notification provider.

Scope

This PR does not modify T3 Code or change Code-Notify's default wording, emoji, delivery channels, suppression rules, or fallback behavior.

Testing

• Extended tests/test-codex-notify.sh with a temporary T3 SQLite fixture.
• Covered exact thread-ID matching, an unrelated malformed runtime payload, missing-T3 fallback, existing CLI fallback, and Codex Desktop duplicate suppression.
• make test: 28 passed, 0 failed.