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/models.py

@@ -26,6 +26,8 @@ class HostAgentRegistration(Base):
     kernel = Column(String(128), nullable=True)
     distro = Column(String(128), nullable=True)
     arch = Column(String(32), nullable=True)
+    # Agent-reported primary IP. 45 chars = max textual IPv6 (no zone suffix).
+    host_ip = Column(String(45), nullable=True)
     last_seen_at = Column(DateTime(timezone=True), nullable=True)
     created_at = Column(DateTime(timezone=True), nullable=False, default=_utcnow)
     updated_at = Column(DateTime(timezone=True), nullable=False,