P8(2): inbound node reassignment (move) with backend re-homing

An inbound's 部署到 node can now be changed after creation; the row,
clients, client_traffics and subscription output stay untouched (same
inbound id throughout).

Contract: the update payload's nodeId counts only when the key was
explicitly sent — the controller probes the raw JSON body and sets
Inbound.NodeIDProvided; the wire adapter now always emits nodeId (null =
local) so clearing the picker is an explicit move-to-local, while
callers that omit nodeId keep the stored assignment (legacy behaviour).

UpdateInbound resolves the target before the port-conflict check (so
conflicts are scoped to the target node), rejects moves to a missing
node, re-derives auto tags under the target node's prefix, validates
the tag against the target node's namespace, and marks BOTH nodes
dirty: the source node's next reconcile sweeps the old tag (no silent
ghost — the flag persists until a reconcile succeeds, so an offline
side just defers), the target's pushes the inbound. Agent-bound nodes
converge via GetXrayConfigForAgent on the agent's next config poll.
A local side has no reconcile loop, so it is applied directly
post-commit (Del/Add on the local runtime, restart fallback).

Frontend: the deploy-to Select is no longer disabled in edit mode
(protocol stays locked); candidate rules unchanged (online nodes only).

Tests: panel->panel move with reconcile sweep/push assertions,
auto-tag prefix regeneration, agent-config flip in both directions,
omitted-nodeId legacy contract, same-node no-op, missing-node
rejection, node->local move.

internal/web/controller/inbound.go

@@ -1,7 +1,9 @@
 package controller
 
 import (
+	"bytes"
 	"encoding/json"
+	"io"
 	"net"
 	"strconv"
 	"strings"
@@ -222,6 +224,27 @@ func (a *InboundController) bulkDelInbounds(c *gin.Context) {
 	notifyClientsChanged()
 }
 
+// requestHasJSONKey reports whether the request body is a JSON object that
+// explicitly carries key — present with a null value counts. The body is
+// restored so the normal bind can read it again. Non-JSON bodies (form
+// posts) report false for every key.
+func requestHasJSONKey(c *gin.Context, key string) bool {
+	if c.Request == nil || c.Request.Body == nil {
+		return false
+	}
+	body, err := io.ReadAll(c.Request.Body)
+	if err != nil || len(body) == 0 {
+		return false
+	}
+	c.Request.Body = io.NopCloser(bytes.NewReader(body))
+	var probe map[string]json.RawMessage
+	if json.Unmarshal(body, &probe) != nil {
+		return false
+	}
+	_, ok := probe[key]
+	return ok
+}
+
 // updateInbound updates an existing inbound configuration.
 func (a *InboundController) updateInbound(c *gin.Context) {
 	id, err := strconv.Atoi(c.Param("id"))
@@ -232,13 +255,16 @@ func (a *InboundController) updateInbound(c *gin.Context) {
 	inbound := &model.Inbound{
 		Id: id,
 	}
+	// An explicitly sent nodeId (even null) is a (re)assignment request —
+	// UpdateInbound migrates the inbound when it differs from the stored
+	// assignment. An omitted nodeId keeps the stored assignment, so detect
+	// the key's presence on the raw body before binding consumes it.
+	nodeIDProvided := requestHasJSONKey(c, "nodeId")
 	if !middleware.BindAndValidateInto(c, inbound) {
 		return
 	}
-	// Same NodeID=0 → nil normalisation as addInbound. UpdateInbound
-	// loads the existing row's NodeID from DB anyway (Phase 1 doesn't
-	// support migrating an inbound between nodes), but normalising here
-	// keeps the wire shape consistent.
+	inbound.NodeIDProvided = nodeIDProvided
+	// Same NodeID=0 → nil normalisation as addInbound.
 	if inbound.NodeID != nil && *inbound.NodeID == 0 {
 		inbound.NodeID = nil
 	}