chore(config): retire unread keys [dynamic], [evidence], [variants], [models] patcher

Nothing in src reads config.dynamic, config.evidence or config.variants, and
[models] patcher was only echoed into harness.json. They now go through the
existing RETIRED_KEYS mechanism and fail with RetiredConfigError naming why
("retired 2026-10-02 because nothing ever read it: ..."); RETIRED_KEYS now
carries the full reason per key so the HarnessX entries keep their wording.

- DynamicConfig, EvidenceConfig, VariantsConfig and their loaders removed;
  ModelConfig.patcher removed. resolved_config.json loses those sections.
- harness.json keeps its shape: model_roles.patcher is always null.
- RELEASE_NOTES "Unreleased" lists the keys and the output shape change.
- Delete .opencode/skills/openultrasast-kiro-impl: it pointed agents at the
  retired openrouter-sast-harness tasks.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/test_opencode_skills.py

@@ -9,7 +9,6 @@ def test_project_opencode_skills_have_required_frontmatter() -> None:
 
     assert {path.parent.name for path in skill_files} == {
         "openultrasast-fix-audit",
-        "openultrasast-kiro-impl",
         "openultrasast-scan",
         "openultrasast-triage",
     }