docs: condense and verify AGENTS.md - #44

Intent

• AGENTS.md had accreted into a flat 18.7KB wall of bullets - hard to scan, and carrying claims nobody had re-checked against the code.
  • Every claim was verified against the current source before being kept; nothing was found stale, so this is a restructure and tighten, not a correction.
  • Reorganised into sections (build/test/release, fields & enums, stream lifecycle, vehicle config, energy sites) so a contributor can jump to the area they're touching.
  • Test-file references, previously scattered as trailing sentences across a dozen bullets, are collapsed into one table.
• 18,714 → 12,707 bytes (-32%). Removed classes of content: narrative rationale already stated verbatim in code comments (stream.py and vehicle.py are heavily commented), duplicated facts stated in two or three bullets, history phrasing ("used to control this", "no longer exists"), and detail re-derivable from the workflow files.
• Every "must never"/"must always" contract is preserved verbatim or tighter: the top-level-workflow requirement for PyPI trusted publishing, the env-context parse error, _close_response() vs close(), the sorted-snapshot dispatch order, the id-not-site_id filter on energy_totals, ingest's no-dedup/no-ranking contract, and the stand-in duck-typing requirement.

Docs only - no code changed. All 12 test scripts pass locally.

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https://claude.ai/code/session_018GNMQ3ZKV6TfQhXKM4AzDu