MANUAL RUN: check codex, pi and opencode JSON usage against a live run #1135

Follow-up to #1118. codeSplitter now reads token usage from the JSON output of codex (exec --json), pi (--mode json) and opencode (run --format json). The shapes come from each CLI's own code: the codex-sdk ThreadEvent types, pi's docs/json.md, and the emitter in opencode run. None of the three was logged in on the agent's machine, so they haven't been checked against a live run yet (codex returned 401, pi had no key, and opencode's free tier refuses runs outside its own app).

With each CLI logged in, run one agent task through codeSplitter and check:

• the run's ~N tokens line is close to what the provider's dashboard shows for that call
• the reply (and any DONE/NEXT note) comes through as text, not JSON

If a shape is off, fix usageOf in apps/codesplitter/src/budget.ts and its test.

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