fix: resolve pip packages from site-packages instead of agent dir

When `pip install --target .` is run inside the hermes-agent checkout,
third-party package directories (openai/, pydantic/, requests/, etc.)
end up alongside real Hermes source files. With the agent dir at the
front of sys.path (insert(0)), Python resolves imports from those local
directories, breaking whenever the host platform differs from the
container (e.g. macOS .so files inside a Linux image).

Fix: append agent dir to sys.path instead of prepending. This lets
site-packages resolve pip packages correctly while still allowing
Hermes-specific modules (run_agent, hermes/, etc.) to resolve since
they do not exist in site-packages.

Also improves verify_hermes_imports() to surface the actual exception
message in startup logs, making it much easier to diagnose why a
module failed to import.

server.py

@@ -61,9 +61,11 @@ def main():
 
     print_startup_config()
 
-    ok, missing = verify_hermes_imports()
+    ok, missing, errors = verify_hermes_imports()
     if not ok and _HERMES_FOUND:
         print(f'[!!] Warning: Hermes agent found but missing modules: {missing}', flush=True)
+        for mod, err in errors.items():
+            print(f'     {mod}: {err}', flush=True)
         print('     Agent features may not work correctly.', flush=True)
 
     STATE_DIR.mkdir(parents=True, exist_ok=True)