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

app/api/incidents/route.ts

@@ -182,9 +182,9 @@ export async function POST(request: Request) {
   // Embed description asynchronously for future similarity search
   const supabaseForEmbed = supabase
   import('@/lib/settings').then(({ getApiKey }) =>
-    getApiKey(supabaseForEmbed, 'VOYAGE_API_KEY').then(voyageKey =>
+    getApiKey(supabaseForEmbed, 'GOOGLE_AI_API_KEY').then(googleAiKey =>
       import('@/lib/claude/embed').then(({ embedText }) =>
-        embedText(input.description.trim(), voyageKey).then(embedding =>
+        embedText(input.description.trim(), googleAiKey).then(embedding =>
           supabase.from('incidents').update({
             embedding: `[${embedding.join(',')}]` as unknown as string,
           }).eq('id', incident.id)