feat(host_agent): agent reports its primary IP; mirror into Host.address (task 274)

The agent now detects its own primary non-loopback IP (UDP-socket trick, no
packets sent) and sends it in the metadata bag; bumps AGENT_VERSION 1.0.0->1.1.0
and re-detects on SIGHUP. The server persists it on HostAgentRegistration.host_ip
and mirrors it into Host.address ONLY when that field is blank — an admin-typed
address is never overwritten. The reported IP shows in the settings table so
admins can see drift regardless.

- agent.py: detect_primary_ip(); host_ip in collect_metadata(); refresh on reload
- routes.py: pure pick_host_address() helper; ingest persists host_ip + mirrors
- models.py + migration host_agent_002_host_ip: new String(45) column
- settings_list.html: Reported IP column
- plugin.yaml: 1.0.0 -> 1.1.0
- tests: pick_host_address (fill-when-blank / never-clobber / no-op),
  detect_primary_ip (never raises, non-loopback), metadata carries host_ip

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

plugins/host_agent/migrations/versions/host_agent_002_host_ip.py

@@ -0,0 +1,24 @@
+# plugins/host_agent/migrations/versions/host_agent_002_host_ip.py
+"""host_agent: add agent-reported host_ip column
+
+Revision ID: host_agent_002_host_ip
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "host_agent_002_host_ip"
+down_revision: Union[str, None] = "host_agent_001_initial"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "host_agent_registrations",
+        sa.Column("host_ip", sa.String(45), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("host_agent_registrations", "host_ip")