release: stamp v0.50.277 + Opus SHOULD-FIX (production-path regression guard)

CHANGELOG, ROADMAP, TESTING bumped (3925 → 3929 tests collected).

Opus SHOULD-FIX absorbed in-release: tests #1-3 documented the dedup
contract via direct construction but did not invoke get_models_grouped().
Test #4 (test_get_models_grouped_unconfigured_providers_get_independent_dicts)
inspects the live source for the literal copy.deepcopy(auto_detected_models)
call AND runs an end-to-end smoke of the fixed assignment loop.

A future refactor that removes the deepcopy at api/config.py:2078 will
fail this test immediately.

ROADMAP.md

@@ -3,7 +3,7 @@
 > Goal: Full 1:1 parity with the Hermes CLI experience via a clean dark web UI.
 > Everything you can do from the CLI terminal, you can do from this UI.
 >
-> Last updated: v0.50.276 (May 03, 2026) — 3925 tests collected
+> Last updated: v0.50.277 (May 03, 2026) — 3929 tests collected
 > Tests: `pytest tests/ --collect-only -q`
 > Source: <repo>/