feat(scaffold-core): codegen/ module — routes, files, wrangler generators

[stackbilt-admin]

Part of #212.

Scope

Extract all code generation from stackbilt-web/src/lib/scaffold-core.ts into packages/scaffold-core/src/codegen/. This is the largest module — approximately 1,000 lines of pattern-specific file generation logic.

Files to create

File	Source	Responsibility
routes.ts	buildRoutes(), routeContent()	Route list derivation from traits; per-pattern route handler bodies
files.ts	baseFiles()	Orchestrator — assembles full ScaffoldFile[] from all generators
wrangler.ts	generateWranglerBindings()	wrangler.toml binding block generation
index.ts	—	Re-exports generateFiles(classification, governance, profile, intention) → ScaffoldFile[]

Dependencies

• classify/ (ClassifyResult, QualityProfile, traits)
• governance/ (GovernanceDocs — governance files are included in the output file set)

Tests

Per-pattern file set assertions:

• workers-saas produces D1 migration, tenant middleware, typed contract
• stripe-webhook produces HMAC verifier, KV idempotency guard
• ai-chat produces streaming handler, system prompt, cost cap middleware
• cron-worker produces scheduled handler, idempotency cursor
• All patterns produce wrangler.toml, src/worker.ts, package.json

Migrate stackbilt-web/src/lib/__tests__/scaffold-materializer-parity.test.ts here.

[stackbilt-admin]

Work shipped in @stackbilt/scaffold-core@1.1.0 (charter#212, PRs #219-222). Closing stale tracking issue.