fix(docs): stop next dev writing untracked AGENTS.md / CLAUDE.md into apps/docs (#10780)

`next dev` (Next 16.3.1) runs `ensureAgentRulesForDev` on boot and, whenever it
detects an AI coding agent, scaffolds `apps/docs/AGENTS.md` and
`apps/docs/CLAUDE.md`. Neither path is tracked or ignored, so both land as `??`
and any `git add -A` after booting the docs server sweeps them into an unrelated
PR.

Those two filenames are load-bearing here: the root `AGENTS.md` is the binding
playbook and agents are told to read the `AGENTS.md` governing the files they
touch. A Next-authored stub pointing at `node_modules/next/dist/docs/` can be
read as this repo's discipline, and its own text argues for committing itself.
The generated `CLAUDE.md` is the single line `@AGENTS.md`, an import directive
that pulls the stub in.

Set `agentRules: false` in `apps/docs/next.config.mjs`, turning generation off at
the source rather than gitignoring the paths: an ignore rule for
`apps/docs/AGENTS.md` would silently swallow a future repo-authored `AGENTS.md`
for this app, failing invisibly at exactly the moment someone was adding real
guidance there.


Claude-Session: https://claude.ai/code/session_01DdCnBGcHeufjrq7drTD3wt

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

apps/docs/next.config.mjs

@@ -6,6 +6,28 @@ const withMDX = createMDX();
 /** @type {import('next').NextConfig} */
 const config = {
   reactStrictMode: true,
+  // `next dev` otherwise writes `apps/docs/AGENTS.md` and `apps/docs/CLAUDE.md`
+  // into the working tree whenever it detects an AI coding agent (Next 16
+  // `ensureAgentRulesForDev`). Neither path is tracked or ignored, so both land
+  // as `??` and any `git add -A` after booting the docs server sweeps them into
+  // an unrelated PR. Those two filenames are load-bearing in this repo: the
+  // root `AGENTS.md` is the binding playbook and agents are told to read the
+  // `AGENTS.md` governing the files they touch, so a Next-authored stub
+  // pointing at `node_modules/next/dist/docs/` can be read as this repo's
+  // discipline -- and the generated text argues for committing itself, which
+  // nudges an agent the wrong way. The generated `CLAUDE.md` is the single
+  // line `@AGENTS.md`, an import directive that pulls the stub in.
+  //
+  // Disabled at the source rather than gitignored on purpose: an ignore rule
+  // for `apps/docs/AGENTS.md` would silently swallow a future repo-authored
+  // `AGENTS.md` for this app, failing invisibly at exactly the moment someone
+  // was trying to add real guidance there. A visible untracked file is a better
+  // failure than an invisibly ignored one for this filename specifically.
+  //
+  // This only stops future generation: a checkout that already ran `next dev`
+  // keeps its copies until they are removed once by hand
+  // (`rm -f apps/docs/AGENTS.md apps/docs/CLAUDE.md`).
+  agentRules: false,
   // No `output: 'standalone'` here on purpose. The standalone packer
   // (`writeStandaloneDirectory` -> `copyTracedFiles`) opens
   // `.next/next-server.js.nft.json`, and that open is the ONLY thing in a