feat(proxy/store): read billing buckets and outcome signals from transcripts

The learn v3 detectors need three things the session scanners did not yet
surface: per-model provider-counted usage split into disjoint billing buckets,
per-turn hook and subagent metadata, and enough repo/commit context to join a
session to its outcome. Extend the Claude, Codex, Gemini and opencode adapters
plus the shared scan state to carry them.

Anthropic and opencode report disjoint buckets; OpenAI and Gemini report
inclusive totals and are normalized on read, so a downstream consumer never has
to know which convention an adapter used.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>