docs: refresh package list + Read first refs after optional-package extraction

- CLAUDE.md project-overview lists must-have core packages (shared/cms/api)
  separately from the four optionals (realtime/events/trpc/ui) with their
  scaffold command. Read first list adds template-tiers.md and notes that
  the events + realtime guides require their package to be scaffolded first.
- overview.md "Five tags" updated: core-composition is 2 must-have plus
  trpc (optional); core is 1 must-have plus ui/realtime/events (optional).
- dependency-flow.md fix: replaces the stale `// in packages/core-trpc`
  example with `// in packages/core-shared` (core-trpc is now optional and
  may not exist in a slim template).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/architecture/dependency-flow.md

@@ -74,7 +74,7 @@ import { ArticleNotFoundError } from "@repo/blog";   // ❌ core → feature
                                                      // constructors as args from features —
                                                      // core-shared never imports them)
 
-// in packages/core-trpc
+// in packages/core-shared (or any non-composition core package)
 import { someBlogThing } from "@repo/blog";          // ❌ core → feature (only core-api/core-cms have exception)
 
 // in apps (using the wrong subpath)