docs: surface turbo gen feature in AGENTS.md and CLAUDE.md

Wires the existing turbo gen feature generator into AGENTS.md (Adding
a Feature section, Key Commands, Specification & Guides) and
CLAUDE.md (Quick Start, Read First). Adds a fast-path callout at the
top of the manual walkthrough in docs/guides/adding-a-feature.md
pointing at scaffolding-a-feature.md.

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

docs/guides/adding-a-feature.md

@@ -4,6 +4,15 @@ A feature is a vertical slice: domain entities, use cases, repositories,
 tRPC router, CMS collection, DI container, and query builders — all owned
 by one package under `packages/<feature>/`.
 
+> **Prefer the generator.** `pnpm turbo gen feature` produces a
+> Lazar-conformant single-entity / single-use-case package matching the
+> `navigation` reference shape (DI, tRPC router with tests, span + capture
+> sandwich, dev seed, contract suite). See
+> [Scaffolding a Feature](./scaffolding-a-feature.md). Use this guide when
+> the generator's Phase-1 scope doesn't fit — multi-entity layouts, custom
+> shapes, or extending an existing feature — or when you need to understand
+> what the generator emits and why.
+
 **New feature or extension?** A new capability gets a new package (e.g.,
 `packages/comments`). Adding an operation to an existing feature (e.g.,
 a `publishArticle` procedure to `packages/blog`) means extending that