docs: template-tiers reference (must-have + optional + generator commands)

docs/architecture/template-tiers.md

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+# Template tiers
+
+This template ships in three tiers:
+
+## Must-have (always present)
+
+- `@repo/core-shared` — protocol types, `BindContext`, instrumentation interfaces, jobs interface, tRPC primitives, payload helpers
+- `@repo/core-eslint` — flat-config preset + repo-rules ESLint plugin + boundaries
+- `@repo/core-typescript` — tsconfig presets (base, react-library, nextjs)
+- `@repo/core-testing` — vitest helpers, factories, mocks, contracts
+- `@repo/core-cms` — Payload config base
+- `@repo/core-api` — top-level tRPC router root (mounts feature routers)
+
+Plus all 5 feature packages: auth, blog, marketing-pages, navigation, media.
+
+## Optional (scaffolded on demand)
+
+| Package | Generator | ADR | Guide |
+|---|---|---|---|
+| core-realtime | `pnpm turbo gen core-package realtime` | ADR-016 | docs/guides/realtime.md |
+| core-events | `pnpm turbo gen core-package events` | ADR-015 | docs/guides/events-and-jobs.md |
+| core-trpc | `pnpm turbo gen core-package trpc` | (none) | (none) |
+| core-ui | `pnpm turbo gen core-package ui` | (none) | (none) |
+
+## Why optional
+
+Each optional package addresses a specific need (realtime delivery, cross-feature events, tRPC, design system). Projects that don't need them get a slimmer template. The generator emits byte-identical copies of the packages as they shipped — see `turbo/generators/__snapshots__/core-package/<name>.snapshot.json` for the canonical content hashes.