fix: recover orphaned DeepSeek key + remove retired settings slots

Migration copies ANTHROPIC_API_KEY value → DEEPSEEK_API_KEY (DeepSeek key
was saved before the rename), then deletes ANTHROPIC_API_KEY and
VOYAGE_API_KEY rows. ALLOWED_KEYS now only lists active provider keys.

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

supabase/migrations/20260713000002_reconcile_settings_keys.sql

@@ -0,0 +1,23 @@
+-- Reconcile app_settings after provider switches:
+-- DeepSeek key was saved under ANTHROPIC_API_KEY slot (before rename) — recover it.
+-- Remove retired ANTHROPIC_API_KEY and VOYAGE_API_KEY slots.
+
+-- Ensure DeepSeek slot exists
+insert into app_settings (key, value) values ('DEEPSEEK_API_KEY', '')
+  on conflict (key) do nothing;
+
+-- Copy orphaned value: ANTHROPIC_API_KEY → DEEPSEEK_API_KEY (only when DEEPSEEK_API_KEY is empty and ANTHROPIC has a value)
+update app_settings dk
+set value = ak.value, updated_at = now()
+from app_settings ak
+where dk.key = 'DEEPSEEK_API_KEY'
+  and ak.key = 'ANTHROPIC_API_KEY'
+  and coalesce(dk.value, '') = ''
+  and coalesce(ak.value, '') <> '';
+
+-- Ensure Gemini slot exists
+insert into app_settings (key, value) values ('GOOGLE_AI_API_KEY', '')
+  on conflict (key) do nothing;
+
+-- Remove retired provider slots
+delete from app_settings where key in ('ANTHROPIC_API_KEY', 'VOYAGE_API_KEY');