feat: API key settings page — store ANTHROPIC/VOYAGE keys in DB with admin UI

- Migration: app_settings table with admin-only RLS (ANTHROPIC_API_KEY, VOYAGE_API_KEY)
- lib/settings.ts: getApiKey() reads DB first, falls back to env var
- lib/claude/client.ts: factory createAnthropicClient(apiKey) replaces singleton
- lib/claude/embed.ts: optional apiKey param, falls back to env
- 3 Claude AI routes + similar route: fetch key from settings before calling AI
- incidents/route.ts: fire-and-forget embed reads VOYAGE key from settings
- GET/POST /api/settings: admin-only masked key management endpoint
- /hse/settings page + ApiKeyForm client component

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FFDuBhMKvoWjrWT3ZnGmmr

lib/claude/client.ts

@@ -1,5 +1,5 @@
 import Anthropic from '@anthropic-ai/sdk'
 
-export const anthropic = new Anthropic({
-  apiKey: process.env.ANTHROPIC_API_KEY ?? '',
-})
+export function createAnthropicClient(apiKey: string): Anthropic {
+  return new Anthropic({ apiKey })
+}