fix: address final review findings for master/agent phase 1 (#6)

- inventory: resolve the image reference via ContainerInspect when a moved
  tag makes ContainerList report the image ID
- store: allow reusing a revoked agent's name (partial unique index) and
  mark the revoked agent's compose/container services removed
- web: publish a services event on revoke; no-store on the one-time token page
- webauth: reject empty OIDC state; accept the CSRF form token from the body only
- agent conn: bound the WebSocket handshake to 30s
- hub: log agent_replaced when a connection replaces an older one

internal/master/hub/hub.go

@@ -78,7 +78,7 @@ func (h *Hub) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	c.SetReadLimit(readLimit)
-	h.register(agent.ID, c)
+	h.register(agent, r.RemoteAddr, c)
 	defer h.unregister(agent.ID, c)
 
 	// Revoking commits revoked_at before calling Disconnect. Re-checking after
@@ -114,12 +114,16 @@ func (h *Hub) Disconnect(agentID int64) {
 	}
 }
 
-func (h *Hub) register(id int64, c *websocket.Conn) {
+// register makes c the agent's live connection, closing any older one. A
+// replacement is logged: it is normal after a network blip, but repeated
+// replacements mean two agents share a token.
+func (h *Hub) register(agent model.Agent, remoteAddr string, c *websocket.Conn) {
 	h.mu.Lock()
-	old := h.conns[id]
-	h.conns[id] = c
+	old := h.conns[agent.ID]
+	h.conns[agent.ID] = c
 	h.mu.Unlock()
 	if old != nil {
+		h.log.Warn("agent_replaced", "agent_id", agent.ID, "agent", agent.Name, "remote_addr", remoteAddr)
 		old.CloseNow()
 	}
 }