feat: Add BetterChat + TimedExecute plugin config modules

- DB migrations 017 (betterchat_configs) and 020 (timedexecute_configs) applied
- TypeORM entities matching production schema exactly
- NestJS modules with full CRUD + apply-to-server + import-from-server
- Pinia stores following teleport config pattern
- BetterChatView: Chat Groups editor with color pickers, font sizes, format strings; Settings tab with word filter, anti-flood, player tagging
- TimedExecuteView: TimerRepeat with presets, RealTime-Timer, OnConnect/OnDisconnect command lists
- Wired into app.module.ts, router, DashboardLayout nav

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/migrations/017_betterchat_configs.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS betterchat_configs (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    license_id UUID NOT NULL REFERENCES licenses(id) ON DELETE CASCADE,
+    config_name VARCHAR(100) NOT NULL,
+    description TEXT,
+    config_data JSONB NOT NULL DEFAULT '{}',
+    is_active BOOLEAN NOT NULL DEFAULT false,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_betterchat_configs_license ON betterchat_configs(license_id);