v2: generate the six manifests, tsconfigs, and knip block from one DAG table

[chughtapan]

Deferred from #891 / PR #893 (Phase 2 scaffolding).

Problem

The v2 dependency DAG is currently written down in four places:

1. scripts/check-architecture-boundaries.js → V2_PACKAGES[*].deps
2. v2/*/package.json → dependencies (six files)
3. v2/*/tsconfig.json → references (six files)
4. knip.json → workspaces["v2/*"].ignoreDependencies (five entries)

check-architecture-boundaries.js pins all four together, so drift in any of
them fails pnpm lint today — that part is covered and proven in PR #893. The
remaining cost is edit burden: adding a package or changing one edge is ~14 hand
edits across 13 files.

Beyond the DAG, the six manifests carry ~130 lines of byte-identical
boilerplate (scripts.{build,lint}, nx.targets.{build,lint}, type, main,
types) differing only by package name and cwd.

Fix recipe

Add scripts/gen-v2-packages.mjs that emits the six package.json files, the
six tsconfig.json files, and the knip.json v2 block from a single table,
then gate it exactly like the existing precedent in package.json:

"arch:config:check": "pnpm arch:config:generate && git diff --exit-code -- 'packages/*/safer-architecture.config.json'"

scripts/gen-architecture-configs.mjs is the shape to copy.

Not in scope

The V2_PACKAGES table itself should stay hand-written. It is a deliberate
transcription of frozen law in docs/architecture/components.md, and the
value of an independent transcription is that drift fails whichever side moves.

[chughtapan]

Filed from PR #893 (Phase 2 scaffolding, #891).