fix: Implement Phase 2 major fixes

Database:
- Add missing indexes for api_key_hash, status, metrics queries
- New migration: 005_add_missing_indexes.sql

Server:
- Fix WebSocket Ping/Pong protocol (RFC 6455 compliance)
- Use separate channel for Pong responses

Agent:
- Replace format!() path construction with PathBuf::join()
- Replace todo!() macros with proper errors for macOS support

Dashboard:
- Fix duplicate filter values in Agents page (__unassigned__ sentinel)
- Add onError handlers to all mutations in Agents, Clients, Sites pages

All changes reviewed and approved.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

projects/msp-tools/guru-rmm/server/migrations/005_add_missing_indexes.sql

@@ -0,0 +1,26 @@
+-- Migration: Add missing indexes for performance
+-- These indexes were identified during code review as missing
+-- Date: 2026-01-20
+
+-- Index for agent API key lookups (authentication)
+-- Supports legacy authentication where agents have their own api_key_hash
+CREATE INDEX IF NOT EXISTS idx_agents_api_key_hash ON agents(api_key_hash);
+
+-- Index for site API key lookups
+-- Note: idx_sites_api_key already exists from migration 002, but using consistent naming
+-- This is a no-op if the index already exists
+CREATE INDEX IF NOT EXISTS idx_sites_api_key_hash ON sites(api_key_hash);
+
+-- Index for command status queries (find all pending/running commands)
+-- Note: idx_commands_agent_status exists for (agent_id, status)
+-- This index is for querying by status alone (e.g., find all pending commands)
+CREATE INDEX IF NOT EXISTS idx_commands_status ON commands(status);
+
+-- Index for metrics time-range queries
+-- Note: idx_metrics_agent_time already exists for (agent_id, timestamp DESC)
+-- This is equivalent - creating with requested name for compatibility
+CREATE INDEX IF NOT EXISTS idx_metrics_agent_timestamp ON metrics(agent_id, timestamp DESC);
+
+-- Index for finding online agents quickly with last_seen ordering
+-- Allows efficient queries like: WHERE status = 'online' ORDER BY last_seen DESC
+CREATE INDEX IF NOT EXISTS idx_agents_status_last_seen ON agents(status, last_seen DESC);