feat: new settings, CLI skeleton and interface skeletons

Adds the pydantic-settings Settings with validated GITEA_URL, OAuth scopes
and toolsets, the argparse CLI skeleton, catalog.model, identity and
GiteaAPIError. Test fixtures now isolate env, cwd and state paths in tmp.

scripts/validate_audit_log.py

@@ -4,10 +4,21 @@
 from __future__ import annotations
 
 import argparse
-import sys
+import os
 from pathlib import Path
 
 from aegis_gitea_mcp.audit import validate_audit_log_integrity
+from aegis_gitea_mcp.config import default_data_dir
+
+
+def default_audit_path() -> Path:
+    """Resolve the audit log path the server would use (env first, then DATA_DIR)."""
+    explicit = os.environ.get("AUDIT_LOG_PATH", "").strip()
+    if explicit:
+        return Path(explicit).expanduser()
+    data_dir = os.environ.get("DATA_DIR", "").strip()
+    base = Path(data_dir).expanduser() if data_dir else default_data_dir()
+    return base / "audit.log"
 
 
 def parse_args() -> argparse.Namespace:
@@ -16,7 +27,7 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         "--path",
         type=Path,
-        default=Path("/var/log/aegis-mcp/audit.log"),
+        default=default_audit_path(),
         help="Path to audit log file",
     )
     return parser.parse_args()