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/policy.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from app.agents.schemas.skills import SkillInjectionMode, SkillShortlistEntry
+
+MAX_SUMMARY_CHARS = 120
+
+
+def choose_injection_mode(score: float, summary_available: bool) -> SkillInjectionMode:
+    if score >= 0.75 and summary_available:
+        return "summary"
+    return "metadata_only"
+
+
+def render_skill_shortlist_context(entries: list[SkillShortlistEntry]) -> str:
+    if not entries:
+        return ""
+
+    lines = ["[Task-Scoped Skills]"]
+    for entry in entries[:3]:
+        detail = entry.summary or "Relevant to the current request."
+        detail = detail[:MAX_SUMMARY_CHARS]
+        lines.append(f"- {entry.skill_name} | mode={entry.injection_mode} | score={entry.score:.2f}")
+        lines.append(f"  {detail}")
+        if entry.matched_terms:
+            lines.append(f"  matched_terms={', '.join(entry.matched_terms[:6])}")
+
+    return "\n".join(lines)