Add CI validation workflow

.github/workflows/validate.yml

@@ -0,0 +1,49 @@
+name: Validate Mika Agent Assist
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+      - "codex/**"
+  workflow_dispatch:
+
+jobs:
+  frontend-build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build frontend
+        run: npm run build
+
+  edge-functions:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Deno
+        uses: denoland/setup-deno@v2
+        with:
+          deno-version: 2.7.14
+
+      - name: Type-check edge functions
+        shell: bash
+        run: |
+          mapfile -t files < <(find supabase/functions -name '*.ts' | sort)
+          deno check --config supabase/functions/deno.json "${files[@]}"