Resolve conflicts from main's FN-6232 single-source triage prompt refactor:
- Drop the inline FAST_TRIAGE_SYSTEM_PROMPT const removed by main; the fast
triage prompt now lives in agent-prompts.ts (planning-fast seam).
- Migrate the PR's no-commit/operational-routing heuristic edits into the
fast block of agent-prompts.ts (standard block already carried them).
- Point triage tests at FAST_PLANNING_PROMPT/TRIAGE_POLICY_PROMPT instead of
the removed const.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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