docs: centralize agent instructions in AGENTS.md (CLAUDE/GEMINI point to it) (#9508)

* docs: centralize agent instructions in AGENTS.md; CLAUDE/GEMINI point to it

- AGENTS.md becomes the single source of truth: full CLAUDE.md content (main
  data) merged with the AGENTS.md-only sections (documentation accuracy,
  repository map, review focus, upstream contributions) and the GEMINI.md-only
  file-placement/root-hygiene and local-access rules. Adds the base-green
  check section (PRs must not be born red) and fixes the stale
  _tasks/release-flow path in Hard Rule 21.
- CLAUDE.md: @AGENTS.md pointer + Claude-Code-only operational deltas
  (EnterWorktree, subagent stash-ban replication, superpowers path overrides,
  base-green/sweep-reds pointers).
- GEMINI.md: pointer + Gemini-only notes; the stale 10-item hard-rule mirror
  is removed (source is the 22-rule list in AGENTS.md).
- ci(release-green): label the not-green tracking issue with base-red.

* docs: retarget docs-sync provider/MCP claims to AGENTS.md and fix test placeholder

---------

Co-authored-by: diegosouzapw <diegosouzapw@users.noreply.github.com>

scripts/check/check-docs-counts-sync.mjs

@@ -259,7 +259,7 @@ export function buildChecks() {
       actual: readProviderTotal(),
       docKey: "providers",
       strict: true,
-      files: ["README.md", "CLAUDE.md"],
+      files: ["README.md", "AGENTS.md"],
     },
     {
       label: "i18n locales count",
@@ -317,9 +317,9 @@ export function buildChecks() {
             skipBefore: /(tools?|definitions?)\s*\(\s*$/i,
             skipAfter: /^\s*\(\d+ CLI/,
           },
-          ["README.md", "CLAUDE.md", "docs/frameworks/MCP-SERVER.md"]
+          ["README.md", "AGENTS.md", "docs/frameworks/MCP-SERVER.md"]
         ),
-        claim(f.mcpScopes, "MCP scopes", { pattern: /(\d+) scopes/gi }, ["README.md", "CLAUDE.md"]),
+        claim(f.mcpScopes, "MCP scopes", { pattern: /(\d+) scopes/gi }, ["README.md", "AGENTS.md"]),
         claim(f.cliTotal, "CLI tools", { pattern: /(\d+) tools(?=\s*\(\d+ CLI)/gi }, ["README.md"]),
       ];
     })(),