feat: Add @codebot help command for instant discoverability

Implements help command that shows all available bot commands with examples and categories.

Users can now type '@codebot help' to see complete command list without reading docs.

tools/ai-review/agents/issue_agent.py

@@ -380,7 +380,9 @@ class IssueAgent(BaseAgent):
         title = issue.get("title", "")
         body = issue.get("body", "")
 
-        if command == "summarize":
+        if command == "help":
+            return self._command_help()
+        elif command == "summarize":
             return self._command_summarize(title, body)
         elif command == "explain":
             return self._command_explain(title, body)
@@ -445,6 +447,68 @@ Be practical and concise."""
         except Exception as e:
             return f"{self.AI_DISCLAIMER}\n\nSorry, I was unable to generate suggestions. Error: {e}"
 
+    def _command_help(self) -> str:
+        """Generate help message with all available commands."""
+        mention_prefix = self.config.get("interaction", {}).get(
+            "mention_prefix", "@codebot"
+        )
+
+        help_text = f"""{self.AI_DISCLAIMER}
+
+## Available {mention_prefix} Commands
+
+### Issue Triage & Analysis
+- `{mention_prefix} triage` - Full issue triage with auto-labeling and priority assignment
+- `{mention_prefix} summarize` - Generate 2-3 sentence summary of the issue
+- `{mention_prefix} explain` - Detailed explanation of what the issue is about
+- `{mention_prefix} suggest` - Solution suggestions or next steps
+- `{mention_prefix} security` - Security-focused analysis of the issue
+
+### Interactive Chat
+- `{mention_prefix} [question]` - Ask questions about the codebase (uses search & file reading tools)
+  - Example: `{mention_prefix} how does authentication work?`
+  - Example: `{mention_prefix} find all API endpoints`
+
+### Setup & Utility
+- `{mention_prefix} help` - Show this help message
+- `{mention_prefix} setup-labels` - Auto-create/map repository labels for auto-labeling
+
+### Pull Request Analysis
+PR reviews run automatically when you open or update a pull request. The bot provides:
+- Inline code review comments
+- Security vulnerability scanning
+- Approval or change-request recommendations
+
+---
+
+### Quick Examples
+
+**Triage an issue:**
+```
+{mention_prefix} triage
+```
+
+**Get help understanding:**
+```
+{mention_prefix} explain
+```
+
+**Ask about the codebase:**
+```
+{mention_prefix} how does the authentication system work?
+```
+
+**Setup repository labels:**
+```
+{mention_prefix} setup-labels
+```
+
+---
+
+*For full documentation, see the [README](https://github.com/YourOrg/OpenRabbit/blob/main/README.md)*
+"""
+        return help_text
+
     def _command_triage(self, context: AgentContext, issue: dict) -> str:
         """Perform full triage analysis on the issue."""
         title = issue.get("title", "")