[feat] Codex CLI token source

[ikseong00]

Goal

Add a TokenSource implementation that captures token usage from OpenAI's Codex CLI, so Tokie grows from Codex usage too — not just Claude Code.

Why

The project is designed around the TokenSource interface explicitly so multiple AI CLI tools can feed the same pet. Codex is the obvious next source. The pet's "diet" expands and users who use both tools get a unified view.

Acceptance

• New file core/tokenSource/codex.ts implementing the TokenSource interface (id, start, stop, optional install).
• Source emits TokenEvent for each detected Codex turn with tokens populated.
• Dedup key uses Codex's message/request id (or sourceId-prefixed hash if unavailable).
• Wired into SourceRegistry in electron/bootstrap.ts.
• Unit tests in core/tokenSource/codex.test.ts — parser / cursor / dedup behavior.
• docs/01-tokens.md updated with Codex section.

Hints

• Reference implementations: core/tokenSource/claudeStatusLine.ts (push / HTTP) and core/tokenSource/claudeJsonl.ts (pull / file watch). Pick whichever pattern fits Codex's surfaces — probably JSONL-style log watching unless Codex has a hook similar to Claude's statusLine.
• Codex CLI stores logs somewhere similar to ~/.config/codex/ or ~/.codex/ — investigate.
• Make sure the cursor persistence path uses a distinct key (e.g. codex-jsonl-files) in lastCursors so it doesn't collide with Claude's.

Out of scope

• UI changes (the pet sprite/badge already shows aggregate state — no Codex-specific visual indicator).
• Multi-source per-AI breakdown in stats panel (separate issue if wanted).