fix: generate complete Next TypeScript scaffold

[rogerchappel]

Summary

• generate .gitignore, next-env.d.ts, and tsconfig.json as part of next-app initialization
• match the Next.js 16 TypeScript metadata contract before any framework command runs
• regression-test that install, lint, build, audit, and repository validation leave the generated scaffold clean
• document the generated TypeScript metadata

Commits

• 92ee920 fix: generate complete Next TypeScript metadata
• a359845 test: keep generated Next scaffold immutable
• 8d9e9a9 docs: list generated Next TypeScript files

Verification

• corepack pnpm install --frozen-lockfile
• corepack pnpm run release:check
• git diff --check origin/main...HEAD

The smoke test verifies the files exist immediately after stackforge init, commits the pristine generated tree, and requires an empty git status --porcelain after npm ci --ignore-scripts, lint, build, audit, and scripts/validate.sh. The verified build no longer reports that Next.js created or reconfigured tsconfig.json.

[rogerchappel]

Automated merge note

Triage class: auto-merge
Summary: Generate complete Next TypeScript scaffold metadata and assert the generated project remains clean after validation (3 files, +64/-5).
Checks run: GitHub Repository hygiene, Docs hygiene, and Generate branchbrief all SUCCESS; isolated worktree corepack pnpm install --frozen-lockfile, corepack pnpm run release:check, and git diff --check origin/main...HEAD passed.
Rebased/CI-repaired: No.
Verified head SHA: 8d9e9a9