annoucement banners, calendar pdf export, vehicle booking quck-add, even quick-add

backend/src/database/migrations/025_create_announcement_banners.sql

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+CREATE TYPE banner_level AS ENUM ('info', 'important', 'critical');
+
+CREATE TABLE IF NOT EXISTS announcement_banners (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  message TEXT NOT NULL,
+  level banner_level NOT NULL DEFAULT 'info',
+  starts_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  ends_at TIMESTAMPTZ,
+  created_by UUID REFERENCES users(id) ON DELETE SET NULL,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_banners_active ON announcement_banners (starts_at, ends_at)
+  WHERE ends_at IS NULL OR ends_at > NOW();