#225 docs(g51): signed base-controlled amendment plan aligned to G53

G51 — Base-controlled AF-02 amendment path (planning only)

Replaces the unsigned/no-DCO historical PR #188 with an independently
signed GitHub commit based on the current canonical main.
This does NOT activate an AF-02 authority change.

Scope and authority boundaries

• Adds precisely five Markdown Spec Kit files to
  specs/051-af02-governance-amendment-path/ (spec, plan, tasks,
  threat-model, consistency). All production source, Cargo files,
  workflows, AF-02 frozen authority, live rulesets and donor records
  remain unchanged.
• Retains the base-built verifier, anti-self-authorization, prior
  amendment record merged into the base before the protected edit,
  exact Git blob OID binding, source-object verification, stale
  evidence rejection, strict founder FD-1 specific permission for
  any one-time bootstrap and a separate FD-2 ruleset-activation gate.
• Reconciles the live, founder-approved G53 zero-human-review
  policy: ruleset 21652974 currently has required approvals 0,
  Code Owner/last push/stale review gates false, and normal
  pull-request merge-only. Ruleset 21652953 separately requires
  strict exact-head rust, assurance-proof, scorecard, deletion and
  non-fast-forward guards.
• Human/model reviews are optional engineering evidence when
  actually performed, not required merge approvals and never
  fabricated PASS. Removal of mandatory human review is
  not permission to bypass the protected-base AF-02 gate.
• Historical AF-02 v2 one-review observation stays immutable and
  distinct from the current GitHub policy.
• Explicitly leaves issues #100 and #215 OPEN; no claim of
  one-time founder FD-1, FD-2, G51 implementation, or
  approval of candidate-only amendment records.

Proof and admission criteria

• Signed GitHub commit 9792ddf922da5e3a4fb5046a3e975addcb1d145d:
  verified signature and DCO true.
• git diff --check PASS; only new planning Spec Kit documents changed.
• Live ruleset readback: 21652974 zero approvals/merge-only,
  21652953 required rust, assurance-proof, scorecard.
• Final exact-head GitHub CI must be successful with no genuine
  failure, then normal guarded merge commit, followed by new main
  assurance verification.
• The earlier unsigned historical PR #188 is not mergeable
  under the signed-commit/DCO discipline. This is a forward
  replacement; there is no force push, squash or rebase.

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Summary by cubic

Adds the planning-only G51 Spec Kit that documents a signed, base-controlled AF-02 amendment path. No production files, workflows, or rulesets are modified; the plan remains a candidate and grants no execution authority.

• Reconciles the live G53 zero-human-approval ruleset with existing exact-head rust/assurance/scorecard CI gates.
• Describes the two-PR amendment mechanism, one-time founder FD-1 bootstrap boundary, and separate FD-2 activation.
• Does not close issues #100 or #215 and does not change the existing base verifier.