feat(skills): add per-task skill spec auto-detection and injection

Replace external inject-spec.py hook with built-in zero-config skill
detection in codeagent-wrapper. The system auto-detects project type
from fingerprint files (go.mod, package.json, etc.), maps to installed
skills, and injects SKILL.md content directly into sub-agent prompts.

Key changes:
- Add DetectProjectSkills/ResolveSkillContent in executor/prompt.go
- Add Skills field to TaskSpec with parallel config parsing
- Add --skills CLI flag for explicit override
- Update /do SKILL.md Phase 4 with per-task skill examples
- Remove on-stop.py global hook (not needed)
- Replace inject-spec.py with no-op (detection now internal)
- Add 20 unit tests covering detection, resolution, budget, security

Security: path traversal protection via validSkillName regex,
16K char budget with tag overhead accounting, CRLF normalization.

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

skills/do/hooks/hooks.json

@@ -1,5 +1,5 @@
 {
-  "description": "do loop hook for 5-phase workflow",
+  "description": "do loop hooks for 5-phase workflow",
   "hooks": {
     "Stop": [
       {
@@ -10,6 +10,17 @@
           }
         ]
       }
+    ],
+    "SubagentStop": [
+      {
+        "matcher": "code-reviewer",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/verify-loop.py"
+          }
+        ]
+      }
     ]
   }
 }