feat: multi-provider AI support with per-provider model selection

- Add llm-factory.ts: unified LLM provider abstraction (Google/Claude/OpenAI)
- Install @langchain/anthropic and @langchain/openai packages
- resolveAiProvider picks active provider from DB settings (Claude > OpenAI > Google)
- All AI graphs (reminder, new-patient, reschedule, internal-chat) now accept provider+model params
- Add claudeAiModel, openAiModel, googleAiModel columns to ai_settings table
- New PUT /api/ai/provider-model route to save selected model per provider
- UI model dropdowns for Claude (Haiku/Sonnet/Opus), OpenAI (GPT-5.x series), Google (Gemini 2.5/3.x)
- Google AI section also gets model selector alongside existing API key field

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/shared/schemas/objects/AiSettingsUncheckedCreateWithoutUserInput.schema.ts

@@ -10,6 +10,9 @@ const makeSchema = () => z.object({
   openAiEnabled: z.boolean().optional(),
   claudeAiKey: z.string().optional(),
   claudeAiEnabled: z.boolean().optional(),
+  claudeAiModel: z.string().optional(),
+  openAiModel: z.string().optional(),
+  googleAiModel: z.string().optional(),
   dentalMgmtKey: z.string().optional(),
   dentalMgmtEnabled: z.boolean().optional(),
   afterHoursEnabled: z.boolean().optional(),