chore(deps): defer Prisma major updates pending coordinated upgrade ADR (#39)

## Summary
Renovate kept proposing Prisma 7 even though we deliberately downgraded to Prisma 6 in #3 — `nestjs-prisma@0.27.0` is incompatible with Prisma 7's driver-adapter contract, and the upgrade is non-trivial enough to warrant its own ADR rather than a silent Renovate merge.

- **`renovate.json`** — add `enabled: false` packageRule for `matchUpdateTypes: ["major"]` on `prisma`, `@prisma/*`, `nestjs-prisma`. Patch and minor bumps of the 6.x line keep flowing.
- **ADR-0006** — new "Prisma version pin: 6.x in v1" subsection records the narrowing of "latest stable major" to 6.x and the two triggers for revisiting:
  1. `nestjs-prisma` ships a release supporting Prisma 7, or
  2. We decide to drop `nestjs-prisma` for a hand-rolled `PrismaModule`.

  Either path needs its own ADR (schema, client instantiation, request-scoped lifecycle all to re-validate).

## Test plan
- [ ] Once merged, the open Prisma 7 PR can be closed (see closure comment below) and won't be recreated.
- [ ] Next Renovate run confirms no Prisma-major PR is created (check the dependency dashboard issue).
- [ ] Next patch/minor of Prisma 6.x still produces a normal grouped "Prisma" PR.

---------

Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #39

renovate.json

@@ -38,6 +38,12 @@
       "groupName": "Prisma",
       "matchPackageNames": ["prisma", "@prisma/*", "nestjs-prisma"]
     },
+    {
+      "matchPackageNames": ["prisma", "@prisma/*", "nestjs-prisma"],
+      "matchUpdateTypes": ["major"],
+      "enabled": false,
+      "description": "Prisma 7 requires a coordinated upgrade with nestjs-prisma compatibility (Prisma 7 was downgraded to 6 in PR #3 because nestjs-prisma 0.27.0 is incompatible with Prisma 7). Re-enable once a Prisma 7 ADR lands and the wrapper situation is settled — see ADR-0006 §'Prisma version pin: 6.x in v1'."
+    },
     {
       "groupName": "Vitest",
       "matchPackageNames": ["vitest", "@vitest/*", "/^vitest-/"]