feat: switch embeddings from Voyage AI to Google Gemini text-embedding-004

- embedText: call Gemini REST API (768-dim) instead of Voyage (1024-dim)
- Migration: drop+recreate incidents.embedding as vector(768), update
  match_incidents function, swap VOYAGE_API_KEY → GOOGLE_AI_API_KEY in app_settings
- Settings UI: relabel to "Google AI API Key (Embeddings)"
- All call sites updated (incidents POST, similar GET)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CPf5Rc8QPx6V8KLEEgfKEQ

lib/claude/embed.ts

@@ -1,15 +1,18 @@
 export async function embedText(text: string, apiKey?: string): Promise<number[]> {
-  const key = apiKey ?? process.env.VOYAGE_API_KEY
-  if (!key) throw new Error('VOYAGE_API_KEY is not set')
-  const res = await fetch('https://api.voyageai.com/v1/embeddings', {
-    method: 'POST',
-    headers: {
-      'Content-Type': 'application/json',
-      'Authorization': `Bearer ${key}`,
-    },
-    body: JSON.stringify({ input: [text], model: 'voyage-3-lite' }),
-  })
-  if (!res.ok) throw new Error(`Voyage embed failed: ${res.status}`)
-  const json = await res.json() as { data: Array<{ embedding: number[] }> }
-  return json.data[0].embedding
+  const key = apiKey ?? process.env.GOOGLE_AI_API_KEY
+  if (!key) throw new Error('GOOGLE_AI_API_KEY is not set')
+  const res = await fetch(
+    `https://generativelanguage.googleapis.com/v1beta/models/text-embedding-004:embedContent?key=${key}`,
+    {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        model: 'models/text-embedding-004',
+        content: { parts: [{ text }] },
+      }),
+    }
+  )
+  if (!res.ok) throw new Error(`Gemini embed failed: ${res.status}`)
+  const json = await res.json() as { embedding: { values: number[] } }
+  return json.embedding.values
 }