chore: migrate from opencode to trellis 0.5.0-rc.6

- Remove legacy .opencode/ directory and configuration
- Update .trellis/ to v0.5.0-rc.6 structure
- Refactor scripts: modularize common/, remove multi_agent/
- Add new common modules: git.py, io.py, log.py, types.py, etc.
- Update workflow.md and AGENTS.md
- Archive completed migration tasks

.claude/settings.json

@@ -0,0 +1,73 @@
+{
+  "env": {
+    "CLAUDE_BASH_MAINTAIN_PROJECT_WORKING_DIR": "1"
+  },
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "startup",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/session-start.py",
+            "timeout": 10
+          }
+        ]
+      },
+      {
+        "matcher": "clear",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/session-start.py",
+            "timeout": 10
+          }
+        ]
+      },
+      {
+        "matcher": "compact",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/session-start.py",
+            "timeout": 10
+          }
+        ]
+      }
+    ],
+    "PreToolUse": [
+      {
+        "matcher": "Task",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/inject-subagent-context.py",
+            "timeout": 30
+          }
+        ]
+      },
+      {
+        "matcher": "Agent",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/inject-subagent-context.py",
+            "timeout": 30
+          }
+        ]
+      }
+    ],
+    "UserPromptSubmit": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 .claude/hooks/inject-workflow-state.py",
+            "timeout": 5
+          }
+        ]
+      }
+    ]
+  },
+  "enabledPlugins": {}
+}