feat(localfirst): PR2 spikes (Worker/OPFS, migration loader, decisions)

[kattsushi]

Goal

Implement PR2 from openspec/changes/localfirst-infra-v1/tasks.md: de-risk Web Worker bundling + SQLite OPFS worker bootstrap, validate migration loading approach, and close the effect-qb + migration DX decisions.

What’s in this PR

Web spikes

• Route: /spike-localfirst — apps/web/src/routes/spike-localfirst.tsx
  • Worker bundling smoke (Start worker + Ping)
  • SQLite OPFS worker smoke (Start sqlite worker + SELECT 1)
  • Migration loader spike (import.meta.glob raw SQL)
• Worker modules:
  • apps/web/src/spikes/localfirst/worker.ts
  • apps/web/src/spikes/localfirst/sqlite-opfs-worker.ts
  • apps/web/src/spikes/localfirst/migrations/loader.spike.ts
  • apps/web/src/spikes/localfirst/migrations/sql/0001_spike.sql

Dev header support

• Adds COOP/COEP headers for local dev in apps/web/vite.config.ts (needed for SharedArrayBuffer/OPFS perf).

Decisions recorded

• openspec/changes/localfirst-infra-v1/decision-effect-qb.md
• openspec/changes/localfirst-infra-v1/decision-migration-dx.md

Tooling note

• Adjusted root lint-staged to run Ultracite only on JS/TS/CSS/SCSS to avoid failing commits that touch only md/json.

Key outcomes

• Migration loader approach validated: import.meta.glob(..., { as: "raw", eager: true }) works in this Vite/TanStack Start setup.
• effect-qb:
  • SQLite SQL rendering works (see tools/spikes/effect-qb-sqlite.mjs).
  • BUT importing effect-qb into TS code breaks tsgo due to library-internal typecheck errors → rejected for V1 runtime.
• Migration DX: no effect-qb migration CLI found → choose Nx workspace generator for V1.

Verification

• pnpm nx typecheck web
• pnpm nx test web

Review path

1. apps/web/src/routes/spike-localfirst.tsx
2. apps/web/src/spikes/localfirst/sqlite-opfs-worker.ts
3. apps/web/src/spikes/localfirst/migrations/loader.spike.ts
4. Decision docs under openspec/changes/localfirst-infra-v1/

Follow-ups (next PRs)

• PR3 (base: this branch): localfirst-db core contract + in-memory adapter + migration runner tests.