feat: initial corvid — standalone ticket service extracted from homelab-dashboard

Extracts the ticket/attachment system into a reusable pip-installable package.
Centralises homelab MCP server (tickets, attachments, system logs) here.

- corvid package: models, router (make_router factory), config, standalone main
- Alembic migration chain for fresh standalone deployments
- Docker Compose for standalone deployment (port 8090)
- mcp_server.py: moved from homelab-dashboard, CORVID_REPO_PATH configurable

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

alembic/script.py.mako

@@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}