fix: pin the vitest trio exactly, and document the peer/transitive exceptions

Copilot review round 1.

@vitest/browser-playwright declares an EXACT peer on vitest ("vitest":
"4.1.10"), so that package — not the root's range — decides which vitest lands in
clients/web. Dropping web's own vitest declaration left the root free to resolve
4.1.11 while web's peer stayed at 4.1.10, so web's tests ran on one vitest while
loading a @vitest/coverage-v8 provider built against another. Both still passed,
which is the bad part.

vitest and @vitest/coverage-v8 at the root and @vitest/browser-playwright in
clients/web are now pinned exactly to 4.1.10 and move together, the same
discipline as the exact prettier pin (#1790).

The docs also claimed more than the change delivers. npm auto-installs an unmet
peer into the install that needs it, and a client install cannot see the root's
tree — so web's eslint-plugin-react-refresh / -storybook and the TUI's
eslint-plugin-react-hooks each pull a client-local eslint, and web's
Storybook/Vitest stack pulls a local typescript and vitest; @types/express
hoists an @types/node into web and cli. Those copies sit nearer than the root's
and win. AGENTS.md and the local-dev skill now say so, and state what the
consolidation actually buys: one declaration and one place to bump, with
verify:dep-lockstep as the guard that the copies agree.

Signed-off-by: cliffhall <cliff@futurescale.com>

AGENTS.md

@@ -87,7 +87,9 @@ The reasoning behind each of these, and what breaks when it is ignored, is the
 
 - **The MCP SDK packages** — `@modelcontextprotocol/client`, `core`, `server`, `server-legacy`, `ext-apps` — **are declared in the repo-root `package.json` and nowhere else.** So is anything reached only through root-owned code with no manifest of its own (`test-servers/src`, `core/`), aliased to the repo root in `vitest.shared.mts`. The v1 SDK (`@modelcontextprotocol/sdk`) is **not** a dependency of this repo and must not become one.
 - **`dependencies` vs `devDependencies` follows from who consumes it at runtime**, not from where it is declared. Anything `core/` imports at runtime must be a root **`dependency`** — the client builds externalize npm packages and a published install resolves them from the root manifest, where devDependencies are absent.
-- **The shared toolchain is declared once, at the repo root, and in no client manifest.** `eslint`, `@eslint/js`, `typescript-eslint`, `globals`, `prettier`, `typescript`, `vitest`, `@vitest/coverage-v8` and `@types/node` are used by every client's own scripts, and every client reaches the root copy by walk-up — `npm run` puts each ancestor `node_modules/.bin` on `PATH`, and Node and TypeScript resolve modules and `@types` the same way — so a client-side declaration buys nothing and installs a second copy that can drift. It had already drifted before #2196 (`globals` `^17.7.0` at the root against `^17.4.0` in all four clients, `typescript-eslint` `^8.65.0` against `^8.56.1`), and one pin instead of five is what makes the exact `prettier` pin (#1790) mean the format gate cannot return a different verdict per client. These stay **`devDependencies`** — none is consumed at runtime and the tarball ships only each client's `build/`. A tool **one** client uses stays in that client (`tsup`, `tsx`, `vite`, `vite-node`, `playwright`, `storybook`, `happy-dom`, `ink-testing-library`, and the `@types/*` for its own libraries).
+- **The shared toolchain is declared once, at the repo root, and in no client manifest.** `eslint`, `@eslint/js`, `typescript-eslint`, `globals`, `prettier`, `typescript`, `vitest`, `@vitest/coverage-v8` and `@types/node` are used by every client's own scripts, and a client that declares none of them still resolves the root copy by walk-up — `npm run` puts each ancestor `node_modules/.bin` on `PATH`, and Node and TypeScript walk parent `node_modules` / `node_modules/@types` the same way. `clients/launcher` declares no `devDependencies` at all and its `validate` is unchanged. A client-side declaration buys nothing and installs a second copy free to drift, as `globals` (`^17.7.0` root / `^17.4.0` clients) and `typescript-eslint` (`^8.65.0` / `^8.56.1`) had before #2196. These stay **`devDependencies`** — none is consumed at runtime and the tarball ships only each client's `build/`. A tool **one** client runs stays in that client (`tsup`, `tsx`, `vite`, `vite-node`, `playwright`, `storybook`, `happy-dom`, `ink-testing-library`, and the `@types/*` for its own libraries).
+  - ⚠️ **Deleting the declaration does not always delete the copy, and the local copy still wins.** npm auto-installs an unmet **peer** into the install that needs it, and it has no visibility into the root's tree — so a client-only ESLint plugin drags a client-local `eslint` in (`eslint-plugin-react-refresh`/`-storybook` in web, `eslint-plugin-react-hooks` in tui), and web's Storybook/Vitest stack drags in a local `typescript` and `vitest`. A hoisted transitive does the same: `@types/express` puts an `@types/node` in web and cli. Those copies sit *nearer* than the root's and take precedence. The consolidation is therefore about **one declaration and one place to bump**, not about a single copy on disk; what must hold is that the copies **agree**, and `npm run verify:dep-lockstep` is the guard that says so.
+  - ⚠️ **`vitest`, `@vitest/coverage-v8` and web's `@vitest/browser-playwright` are pinned exactly, and move together.** `@vitest/browser-playwright` declares an **exact** peer on `vitest`, so it — not the root range — decides which `vitest` web installs. Left to float, the root resolves a newer patch and web's tests then run on one `vitest` while loading a coverage provider built against another. Bumping means editing all three in one change, the same discipline the exact `prettier` pin (#1790) exists for.
 - **A root-declared package that `core/` imports at runtime must also be named in all three bundler `external` lists** (`clients/{cli,tui}/tsup.config.ts`, `clients/web/tsup.runner.config.ts`), since which client reaches it is a function of what `core/` imports rather than of what the client's own code names. `npm run verify:bundle-externals` enforces this against the **built output**.
 - **A dependency that renders React components must be bundled** into the client that uses it (`noExternal`) and declared only there — an externalized one resolves its own `react` and splits the tree. `ink` is the single exemption, on cost, and it is only safe while the root `react` range stays open to the whole major (`^19.0.0`).
 - **One version per install-crossing dependency.** When bumping a dependency the shared sources pull in, bump it in every install that declares it. Never raise the tsc heap to work around a skew. `npm run verify:dep-lockstep` enforces this.