#229 docs(agents): append verified local Graft guidance without changing governance

Safe, optional local Graft context guidance

Signed+DCO replacement for unsigned PR #169, based on the
current live main rather than its historical agent policy.

• Only appends a marker-fenced optional Graft section to AGENTS.md;
  the complete live AGENTS.md before this edit is preserved byte
  for byte, including founder-approved G53 zero-human-review
  governance, strict technical CI, AF-02 boundaries and
  normal expected-head merging. No deleted or replaced rules.
• Verified installed authorized Mac Graft version 0.21.1,
  documented via actual CLI --help. No local Graft graph exists
  in primary checkout; no graft build/init or model call
  is claimed.
• Explicitly differentiates free local code graph/navigation from
  --deep LLM processing. No paid provider, external API or
  imaginary Graft review evidence.
• Warns that graft init can alter agent config, that caches
  must not be committed, and source verification is mandatory.
• Preserves independent Alibaba OCR/Jev when really runnable.
  Unavailable reviews are NOT_RUN, never invented PASS.
• Signed commit + DCO, all exact-head GitHub technical checks
  and post-merge main proof remain mandatory.
• Original PR #169 must not be merged or rebased because its
  base text incorrectly replaced modern human-review rules
  with obsolete requirements.

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Summary by cubic

Appends a marker-fenced, optional Graft local-context section to AGENTS.md without touching any existing governance, review, or merge rules; every live rule stays byte-for-byte unchanged.

• Documents the verified authorized Mac Graft 0.21.1 via CLI and explicitly claims no local graph build or model call.
• Marks Graft navigation as a read-only aid, recommends graft check before trusting indexed references, and requires validating findings against live source.
• Warns that graft init modifies agent config files, that caches must not be committed, and that graft build --deep or paid external LLM calls need explicit authorization.
• Supersedes the unsigned PR #169, whose base text incorrectly replaced modern human-review rules with obsolete ones.