feat: add image generation model and generate_image agent tool

Bots can now be configured with an image generation model (must have
image-output compatibility). When set, the agent exposes a generate_image
tool that calls the model via Twilight AI SDK, saves the result to the
bot container filesystem, and returns the file path.

- Add image_model_id column to bots table (migration 0053)
- Update settings SQL queries, service, and types
- New ImageGenProvider tool provider in internal/agent/tools/
- Wire provider in both cmd/agent and cmd/memoh entry points
- Add image model selector to frontend bot settings with compat filtering
- Regenerate swagger, SDK types, and sqlc code

db/migrations/0001_init.up.sql

@@ -177,6 +177,7 @@ CREATE TABLE IF NOT EXISTS bots (
   compaction_ratio INTEGER NOT NULL DEFAULT 80,
   compaction_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
   title_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
+  image_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
   tts_model_id UUID REFERENCES tts_models(id) ON DELETE SET NULL,
   browser_context_id UUID REFERENCES browser_contexts(id) ON DELETE SET NULL,
   metadata JSONB NOT NULL DEFAULT '{}'::jsonb,

db/migrations/0053_add_image_model.down.sql

@@ -0,0 +1,3 @@
+-- 0053_add_image_model (rollback)
+-- Remove image_model_id column from bots table
+ALTER TABLE bots DROP COLUMN IF EXISTS image_model_id;

db/migrations/0053_add_image_model.up.sql

@@ -0,0 +1,3 @@
+-- 0053_add_image_model
+-- Add image_model_id column to bots table for image generation model configuration
+ALTER TABLE bots ADD COLUMN IF NOT EXISTS image_model_id UUID REFERENCES models(id) ON DELETE SET NULL;