fix: Fix navigation links and restore LanguageSwitcher

- Add missing nav keys to types.ts, de.ts, en.ts (sessions, buddies, stats, wishlist)
- Add LanguageSwitcher back to authenticated header
- Create /sessions page with SessionList
- Create /buddies page with BuddyList
- Create /stats page with StatsDashboard
- Create /wishlist placeholder page

sql/create_app_banners.sql

@@ -0,0 +1,49 @@
+-- App Banners Table for dynamic hero content on home page
+
+CREATE TABLE IF NOT EXISTS app_banners (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    title TEXT NOT NULL,
+    image_url TEXT NOT NULL,  -- 16:9 Banner Image
+    link_target TEXT,         -- e.g., '/sessions'
+    cta_text TEXT DEFAULT 'Open',
+    is_active BOOLEAN DEFAULT false,
+    created_at TIMESTAMPTZ DEFAULT now(),
+    updated_at TIMESTAMPTZ DEFAULT now()
+);
+
+-- Only one banner should be active at a time (optional constraint)
+CREATE UNIQUE INDEX IF NOT EXISTS idx_app_banners_active 
+    ON app_banners (is_active) 
+    WHERE is_active = true;
+
+-- RLS Policies
+ALTER TABLE app_banners ENABLE ROW LEVEL SECURITY;
+
+-- Everyone can view active banners
+CREATE POLICY "Anyone can view active banners"
+    ON app_banners FOR SELECT
+    USING (is_active = true);
+
+-- Admins can manage all banners
+CREATE POLICY "Admins can manage banners"
+    ON app_banners FOR ALL
+    USING (
+        EXISTS (
+            SELECT 1 FROM admin_users
+            WHERE admin_users.user_id = auth.uid()
+        )
+    );
+
+-- Trigger for updated_at
+CREATE OR REPLACE FUNCTION update_app_banners_updated_at()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = now();
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER trigger_app_banners_updated_at
+    BEFORE UPDATE ON app_banners
+    FOR EACH ROW
+    EXECUTE FUNCTION update_app_banners_updated_at();