Generate seeds each declared pack's Extension contract space

[borisno2]

Parent

#1121 — build spec 1 of the Prisma 8 architecture spec. Lands on the prisma-8 integration branch, not main.

What to build

For every db.extensions entry, pnpm generate derives the /pack, /control and /runtime subpaths from the package name, fails naming the pack and the missing subpath when one is absent, and materialises the pack's contract space under migrations/ through the toolchain's public seed phase between writing prisma.config.ts and emitting. The five files are committed and covered by the dirty-tree check; the root .gitignore stops ignoring prisma/migrations/.

Acceptance criteria

• A pgvector fixture produces the migration package, head ref and snapshot files; a second generate reports them unchanged
• A pack without a /control export fails generate with the pack and subpath named
• The dirty-tree check covers the space's files and snapshot
• .gitignore no longer excludes prisma/migrations/

Blocked by

• The CLI renders the Contract module and prisma.config.ts, shells to contract emit, and deletes the PSL assembly #1134

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Generated by Claude Code