refactor: extract transport-agnostic core and shared tool registry

Introduce aegis_gitea_mcp.registry as the single name->handler source of
truth consumed by every transport adapter, moving TOOL_HANDLERS out of the
FastAPI server module. Add aegis_gitea_mcp.errors.ToolError so core handlers
no longer import fastapi.HTTPException; raw_tools now raises ToolError and the
HTTP adapter maps it back to HTTPException, preserving status codes and audit
behavior. Add a subprocess boundary test asserting the core imports without
pulling in fastapi/uvicorn/starlette.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_raw_api.py

@@ -6,10 +6,10 @@ from pathlib import Path
 from typing import Any
 
 import pytest
-from fastapi import HTTPException
 from pydantic import ValidationError
 
 from aegis_gitea_mcp.config import reset_settings
+from aegis_gitea_mcp.errors import ToolError
 from aegis_gitea_mcp.tools.arguments import (
     extract_repository,
     extract_target_path,
@@ -83,7 +83,7 @@ async def test_lowercase_method_is_normalized(raw_env: None) -> None:
 async def test_delete_denied_when_write_mode_off(raw_env: None) -> None:
     """A write method is denied (no network call) while write-mode is disabled."""
     stub = StubRawGitea()
-    with pytest.raises(HTTPException) as exc_info:
+    with pytest.raises(ToolError) as exc_info:
         await raw_api_request_tool(stub, {"method": "DELETE", "path": "/repos/acme/app/issues/1"})
 
     assert exc_info.value.status_code == 403
@@ -135,7 +135,7 @@ async def test_write_denied_for_repo_outside_whitelist(
     monkeypatch.setenv("WRITE_REPOSITORY_WHITELIST", "acme/other")
 
     stub = StubRawGitea()
-    with pytest.raises(HTTPException) as exc_info:
+    with pytest.raises(ToolError) as exc_info:
         await raw_api_request_tool(stub, {"method": "POST", "path": "/repos/acme/app/issues"})
 
     assert exc_info.value.status_code == 403
@@ -158,7 +158,7 @@ async def test_non_repository_write_denied(monkeypatch: pytest.MonkeyPatch, tmp_
     monkeypatch.setenv("WRITE_REPOSITORY_WHITELIST", "acme/app")
 
     stub = StubRawGitea()
-    with pytest.raises(HTTPException) as exc_info:
+    with pytest.raises(ToolError) as exc_info:
         await raw_api_request_tool(stub, {"method": "POST", "path": "/user/repos"})
 
     assert exc_info.value.status_code == 403
@@ -173,7 +173,7 @@ async def test_non_repository_write_denied(monkeypatch: pytest.MonkeyPatch, tmp_
 async def test_sensitive_paths_denied_on_get(raw_env: None, path: str) -> None:
     """Admin/credential surfaces are denied for every method, including GET."""
     stub = StubRawGitea()
-    with pytest.raises(HTTPException) as exc_info:
+    with pytest.raises(ToolError) as exc_info:
         await raw_api_request_tool(stub, {"method": "GET", "path": path})
 
     assert exc_info.value.status_code == 403
@@ -253,7 +253,7 @@ async def test_raw_api_disabled(monkeypatch: pytest.MonkeyPatch, tmp_path: Path)
     monkeypatch.setenv("RAW_API_ENABLED", "false")
 
     stub = StubRawGitea()
-    with pytest.raises(HTTPException) as exc_info:
+    with pytest.raises(ToolError) as exc_info:
         await raw_api_request_tool(stub, {"method": "GET", "path": "/repos/acme/app"})
     assert exc_info.value.status_code == 403
     assert "disabled" in str(exc_info.value.detail)