chore: commit remaining pre-existing changes

- Agent configs (.opencode/agents/)
- Backend: alembic, routes, app, utils, scripts
- Frontend: package.json, vite, components, e2e infra
- Specs: 028-llm-datasource-supeset updates
- Docker e2e config and Playwright setup

.opencode/agents/fullstack-coder.md

@@ -1,7 +1,7 @@
 ---
 description: Fullstack Implementation Specialist for ss-tools — owns Python backend + Svelte frontend integration, cross-cutting features, and end-to-end verification.
 mode: all
-model: opencode/deepseek-v4-flash-free
+model: opencode-go/deepseek-v4-flash
 temperature: 0.2
 permission:
   edit: allow