chore: consolidate shared toolchain devDependencies into the root package.json

Declare the toolchain every client uses once, at the repo root, and delete the
per-client copies: eslint, @eslint/js, typescript-eslint, globals, prettier and
typescript (all five manifests), plus vitest, @vitest/coverage-v8 and
@types/node (four). Adds the latter three to the root manifest; the first six
were already there.

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 nothing about the client scripts changes. clients/launcher now
declares no devDependencies at all and its validate is unchanged.

The copies had already drifted: globals sat at ^17.7.0 at the root against
^17.4.0 in all four clients, and typescript-eslint at ^8.65.0 against ^8.56.1.
Consolidating takes the root's version in both cases, and makes the exact
prettier pin (#1790) a single pin rather than five that can diverge.

Tools only one client runs stay where they are — tsup, tsx, vite, vite-node,
playwright, storybook, happy-dom, ink-testing-library, and each client's own
@types/*.

Documents the rule in AGENTS.md's Dependency placement section and the reasoning
in the local-dev skill.

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

package.json

@@ -115,13 +115,16 @@
   },
   "devDependencies": {
     "@eslint/js": "^10.0.1",
+    "@types/node": "^24.12.4",
     "@types/proper-lockfile": "^4.1.4",
+    "@vitest/coverage-v8": "^4.1.10",
     "eslint": "^10.8.0",
     "eslint-plugin-react-hooks": "^7.1.1",
     "express": "^5.2.1",
     "globals": "^17.7.0",
     "prettier": "3.8.4",
     "typescript": "~5.9.3",
-    "typescript-eslint": "^8.65.0"
+    "typescript-eslint": "^8.65.0",
+    "vitest": "^4.1.10"
   }
 }