refactor: rename System → Module per ADR-0025

[wmadden-electric]

Mechanical rename of the unit of composition from System to Module, per
ADR-0025.
The unit is now authored with module(), and the App is the outermost Module.
This mirrors the Hex→System sweep ADR-0014 itself performed.

What changed

Code (refactor(app)!) — @prisma/app and its extensions:

• system() → module(); SystemNode → ModuleNode, SystemContext →
  ModuleContext, SystemBuilder → ModuleBuilder, SystemOutputs →
  ModuleOutputs; the node kind discriminant 'system' → 'module'
• load-system.ts → load-module.ts (loadSystem → loadModule); the
  system-*.test files → module-*; side-effect-system/valid-system
  fixtures → *-module
• error messages, doc comments, and test identifiers that named the unit

Examples (refactor(examples)):

• examples/storefront-auth/systems/ → modules/ (pnpm-workspace glob and
  lockfile links follow); system.ts deploy roots → module.ts

Docs:

• README opening now introduces Module without "System"; mermaid System:
  labels → Module:; the hexagonal aside rewritten to introduce Module
• glossary, all docs/design/10-domains/ (incl. system-composition.md →
  module-composition.md), and other design docs
• ADR-0013 and ADR-0016 filenames + titles renamed; System prose swept across
  earlier ADRs (0003, 0006, 0007, 0009, 0015, 0017, 0020, 0022, 0023, 0024);
  decisions README index updated

Non-targets honored (not renamed)

• Package names (@prisma/app*), the prisma-app CLI, prisma-app.config.ts,
  .prisma-app/
• Service and Extension — different registers, unchanged
• Plain-English "system": filesystem, ecosystem, type system,
  build system, documentation system
• ADR-0014 and ADR-0025 are left as-is (the superseded decision and the
  deciding one). The single exception: ADR-0025's cross-link to ADR-0016 was
  updated to the renamed filename so the rename doesn't leave a dangling link —
  URL only, no prose change.

Acceptance

pnpm build, pnpm typecheck, pnpm test, test:types (via turbo), and
pnpm lint all green. grep -riE '\bsystem\s*\(|SystemNode' packages examples docs returns only legitimate uses: plain-English "type system" and the
deliberately-preserved ADR-0014/0025 history.

Coordination

• Stacked on docs: ADR-0025 — the unit of composition is a Module (+ the vocabulary rubric that decided it) #51 (docs/vocabulary-tests, which lands ADR-0025 and the
  vocabulary rubric). This branch is cut from docs: ADR-0025 — the unit of composition is a Module (+ the vocabulary rubric that decided it) #51; merge after docs: ADR-0025 — the unit of composition is a Module (+ the vocabulary rubric that decided it) #51. Once docs: ADR-0025 — the unit of composition is a Module (+ the vocabulary rubric that decided it) #51
  is in main, this PR's diff reduces to the rename alone.
• feat(app-cron): cron as a driver System (S2) #45 (claude/cron-driver-system, the @prisma/app-cron package) is still
  open and not present on this branch. After this rename lands, feat(app-cron): cron as a driver System (S2) #45 must rebase
  onto it — system.ts → module.ts, the cron() helper's return type →
  ModuleNode, and its doc comments.

[pkg-pr-new]

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@prisma/alchemy

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@prisma/app

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@prisma/app-assemble

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@prisma/app-cli

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@prisma/app-cloud

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@prisma/app-nextjs

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@prisma/app-node

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@prisma/app-rpc

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prisma-app

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commit: 4fe415c