agent: add flock.fritzlab.net/addresses annotation (eth0 static IPs)

Like anycast, addresses IPs are advertised via BGP (/128+/32) and get
host routes via the AnycastReconciler. The sole difference: they are
assigned to pod eth0 instead of lo, so workloads that inspect their
primary interface (e.g. Plex remote-access detection) see the public IP
directly.

- annotations.go: annAddresses const, Addresses []net.IP in ParsedAnnotations
- state.go: Addresses []string persisted in allocations.json
- anycast.go: resolveAnycastTargets processes Anycast+Addresses together
- netns_linux.go: configurePodSide assigns Addresses to eth0
- netns_stub.go: mirror Addresses field for non-Linux builds
- handlers.go: thread Addresses through ADD path

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

pkg/agent/state.go

@@ -33,6 +33,7 @@ type Allocation struct {
 	IP6         string          `json:"ip6,omitempty"`
 	IP4         string          `json:"ip4,omitempty"`
 	Anycast     []string        `json:"anycast,omitempty"`
+	Addresses   []string        `json:"addresses,omitempty"`
 	State       AllocationState `json:"state"`
 	AllocatedAt time.Time       `json:"allocated_at"`
 }