feat(skills): enhance skills system with matching and evaluation

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/agents/skills/models.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+
+SkillLifecycleAction = Literal[
+    "created_candidate",
+    "promoted_to_shadow",
+    "promoted_to_active",
+    "degraded_to_deprecated",
+    "retired",
+    "reactivated",
+    "feedback_recorded",
+    "no_change",
+]
+
+
+class SkillLifecycleDecision(BaseModel):
+    skill_name: str
+    action: SkillLifecycleAction
+    previous_status: str | None = None
+    new_status: str
+    reason: str
+    evidence_refs: list[dict[str, object]] = Field(default_factory=list)
+    confidence: float | None = None
+    review_after: datetime | None = None