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

supabase/migrations/20260713000001_gemini_embeddings.sql

@@ -0,0 +1,49 @@
+-- Migrate embeddings from Voyage AI (1024-dim) to Gemini text-embedding-004 (768-dim)
+
+-- Drop dependent objects first
+drop index if exists incidents_embedding_idx;
+drop function if exists match_incidents;
+
+-- Replace column (dimension change requires drop+add)
+alter table incidents drop column if exists embedding;
+alter table incidents add column embedding vector(768);
+
+-- Recreate index
+create index incidents_embedding_idx
+  on incidents using ivfflat (embedding vector_cosine_ops)
+  with (lists = 10);
+
+-- Recreate similarity function at 768-dim
+create or replace function match_incidents(
+  query_embedding vector(768),
+  exclude_id      uuid,
+  match_count     int default 5
+)
+returns table (
+  id            uuid,
+  reference_no  text,
+  incident_type text,
+  description   text,
+  severity      int,
+  similarity    float
+)
+language sql
+security definer
+as $$
+  select
+    i.id,
+    i.reference_no,
+    i.incident_type,
+    i.description,
+    i.severity,
+    1 - (i.embedding <=> query_embedding) as similarity
+  from incidents i
+  where i.id != exclude_id
+    and i.embedding is not null
+  order by i.embedding <=> query_embedding
+  limit match_count;
+$$;
+
+-- Register Gemini key slot, remove Voyage slot
+insert into app_settings (key, value) values ('GOOGLE_AI_API_KEY', '') on conflict (key) do nothing;
+delete from app_settings where key = 'VOYAGE_API_KEY';