feat: add ACP (Agent Client Protocol) server for editor integration

Adds full ACP support enabling hermes-agent to work as a coding agent
inside VS Code (via vscode-acp extension), Zed, JetBrains IDEs, and
any ACP-compatible editor.

## New module: acp_adapter/

- server.py: HermesACPAgent implementing all 15 Agent protocol methods
  (initialize, authenticate, new/load/list/fork/resume session, prompt,
  cancel, set mode/model/config, on_connect)
- session.py: Thread-safe SessionManager with per-session AIAgent lifecycle
- events.py: Callback factories translating hermes callbacks to ACP
  session_update notifications (tool_call, agent_thought, agent_message)
- tools.py: Tool kind mapping (20+ tools → read/edit/execute/search/fetch/think)
  and content builders (diffs for file edits, terminal output, text previews)
- permissions.py: Bridges hermes approval_callback to ACP requestPermission
  RPC for dangerous command approval dialogs in the editor
- auth.py: Provider credential verification
- entry.py: CLI entry point with .env loading and stderr logging

## Integration points

- run_agent.py: ACP tool bridge hook in _execute_tool_calls() for
  delegating file/terminal operations to the editor
- hermes_cli/main.py: 'hermes acp' subcommand
- pyproject.toml: [acp] optional dependency, hermes-acp entry point,
  included in [all] extras (auto-installed via install.sh)

## Supporting files

- acp_registry/agent.json: ACP Registry manifest
- acp_registry/icon.svg: Hermes caduceus icon
- docs/acp-setup.md: User-facing setup guide for VS Code, Zed, JetBrains

## Tests

- 41 new tests across 5 test files covering tools, sessions, permissions,
  server lifecycle, and auth
- Full test suite: 2901 passed, 0 failures

## User flow

1. hermes is already installed (install.sh)
2. Install 'ACP Client' extension in VS Code
3. Configure: command='hermes', args=['acp']
4. Chat with Hermes in the editor — diffs, terminals, approval
   dialogs, thinking blocks all rendered natively

hermes_cli/main.py

@@ -21,6 +21,7 @@ Usage:
     hermes version             # Show version
     hermes update              # Update to latest version
     hermes uninstall           # Uninstall Hermes Agent
+    hermes acp                 # Run as ACP server (editor integration)
     hermes sessions browse     # Interactive session picker with search
 """
 
@@ -2556,6 +2557,27 @@ For more help on a command:
         help="Skip confirmation prompts"
     )
     uninstall_parser.set_defaults(func=cmd_uninstall)
+
+    # =========================================================================
+    # acp command
+    # =========================================================================
+    acp_parser = subparsers.add_parser(
+        "acp",
+        help="Run Hermes Agent as an ACP (Agent Client Protocol) server",
+        description="Start Hermes Agent in ACP mode for editor integration (VS Code, Zed, JetBrains)"
+    )
+
+    def cmd_acp(args):
+        """Launch Hermes Agent as an ACP server."""
+        try:
+            from acp_adapter.entry import main as acp_main
+            acp_main()
+        except ImportError:
+            print("ACP dependencies not installed.")
+            print("Install them with:  pip install -e '.[acp]'")
+            sys.exit(1)
+
+    acp_parser.set_defaults(func=cmd_acp)
     
     # =========================================================================
     # Parse and execute