fix(web): replace actor_id self-event filtering with idempotent cache updates

actor_id identifies the user, not the browser tab. Filtering WS events
by actor_id broke multi-tab sync — other tabs of the same user would
silently miss updates. Instead, make all WS cache handlers idempotent
(dedup checks on add, no-op on duplicate merge/filter) so mutations and
WS events coexist safely without filtering.

- WSClient: pass actor_id to event handlers for future per-handler use
- use-realtime-sync: remove isSelf() gating from onAny and specific handlers
- useCreateIssue: add .some() dedup guard + onSettled invalidation
- use-issue-reactions: remove payload-level self-filter (dedup already present)
- use-issue-timeline: remove payload-level self-filter on comment:created,
  reaction:added, reaction:removed (dedup already present)
- Clean up useCallback deps that no longer reference userId

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

apps/web/shared/api/ws-client.ts

@@ -1,7 +1,7 @@
 import type { WSMessage, WSEventType } from "@/shared/types";
 import { type Logger, noopLogger } from "@/shared/logger";
 
-type EventHandler = (payload: unknown) => void;
+type EventHandler = (payload: unknown, actorId?: string) => void;
 
 export class WSClient {
   private ws: WebSocket | null = null;
@@ -53,7 +53,7 @@ export class WSClient {
       const eventHandlers = this.handlers.get(msg.type);
       if (eventHandlers) {
         for (const handler of eventHandlers) {
-          handler(msg.payload);
+          handler(msg.payload, msg.actor_id);
         }
       }
       for (const handler of this.anyHandlers) {