Add C-380: json.to_map holds one entry per key

[O6lvl4]

Adds C-380 under ALS-C1: json.to_map folds an object's fields into the map one upsert at a time. A repeated key therefore keeps the position of its first occurrence and takes the value of its last, so the map holds it once.

The judge side of almide/almide#3700. On wasm today, json.to_map(value.object([("k", 1), ("k", 2)])) answers ["k": "1", "k": "2"]: len is 2, get returns the first value, and == against ["k": "2"] is false. Native answers ["k": "2"].

• Contract C-380 pins three rules:
  • one entry per key (first position, last value);
  • a Str field is taken verbatim, any other value is its value.stringify text;
  • a non-object is none.
• Fixture spec/wasm_cross/json_to_map_duplicate_keys.almd covers a repeated key, first-position order, mixed non-Str values, a json.parsed duplicate, an empty object, a non-object, and equality against the deduplicated map.
• Reference evaluator fix. json.to_map in the evaluator answered none for any non-Str value and did not deduplicate. It now follows C-380, and its output on the fixture is byte-identical to almide native (develop 5cbe703c5).
• Provenance. Only C-380's row is added. A full --write also rewrites older rows whose entry commits moved when their PRs were rebase-merged, so that unrelated churn is left out.

Gates run locally, all green: check-contracts, contract-provenance, als-element-coverage, als-style, als-validation, links, gate-verification, selftest-conformance, runner-coverage.

The wasm leg of the fixture fails on almide today. That is the defect; the implementation PR follows the pin advance.