Sanitize error responses to prevent internal detail leakage

[7tg]

Summary

• Add safe_error_message() utility that maps known Django exception types (IntegrityError, FieldError, OperationalError, ValidationError, ValueError, TypeError) to generic client-safe messages while logging the real exception server-side
• Replace all 16 instances of raw str(e) in handler error responses across crud.py, actions.py, relations.py, and meta.py
• Add sanitize_pydantic_errors() to strip input, ctx, and url fields from Pydantic validation errors in views.py
• Add 11 new tests verifying that each exception type returns its safe message, real exceptions are logged, and Pydantic error sanitization works correctly

What could leak before this fix

• IntegrityError → table/column names, constraint names
• FieldError → valid field names and model schema
• OperationalError → database host/connection info
• FileNotFoundError → internal file paths
• Pydantic e.errors() → internal field types, input values, context

Test plan

• All 372 tests pass (361 existing + 11 new)
• safe_error_message maps each exception type to its generic message
• Real exception details are logged via logger.exception()
• sanitize_pydantic_errors strips input, ctx, url fields
• No raw str(e) or unsanitized e.errors() remain in source
• Pre-commit hooks pass (ruff, ruff-format, mypy, djlint)

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
django_admin_mcp/views.py	40.00%	3 Missing ⚠️
django_admin_mcp/handlers/actions.py	60.00%	2 Missing ⚠️
django_admin_mcp/handlers/crud.py	80.00%	1 Missing ⚠️

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