feat: add harness skill with hooks install/uninstall support (#156)

Add multi-session autonomous agent harness with progress checkpointing,
failure recovery, task dependencies, and post-completion self-reflection.

- Add harness module to config.json (copy_dir with hooks.json)
- Add 7 hook scripts: stop, sessionstart, teammateidle, subagentstop,
  claim, renew, self-reflect-stop + shared _harness_common.py
- Fix self-reflect-stop: only triggers when harness was initialized
  (checks harness-tasks.json existence), not on every session
- Add unmerge_hooks_from_settings() to uninstall.py for clean hook removal
- Add unit tests (57 tests) and E2E test (100 tasks + 5 self-reflect)

Generated with SWE-Agent.ai

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

skills/harness/hooks/hooks.json

@@ -0,0 +1,60 @@
+{
+  "description": "Harness hooks: prevent premature stop, self-reflection iteration, inject task context on session start, keep teammates working, block subagent stop when tasks remain",
+  "hooks": {
+    "Stop": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/harness-stop.py\"",
+            "timeout": 10
+          }
+        ]
+      },
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/self-reflect-stop.py\"",
+            "timeout": 15,
+            "statusMessage": "Self-reflecting on task completion..."
+          }
+        ]
+      }
+    ],
+    "SessionStart": [
+      {
+        "matcher": "startup|resume|compact",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/harness-sessionstart.py\"",
+            "timeout": 10
+          }
+        ]
+      }
+    ],
+    "TeammateIdle": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/harness-teammateidle.py\"",
+            "timeout": 10
+          }
+        ]
+      }
+    ],
+    "SubagentStop": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/harness-subagentstop.py\"",
+            "timeout": 10
+          }
+        ]
+      }
+    ]
+  }
+}