docs: sync PRs #890-#925 to aeon docs

[aaronjmars]

Syncs merged aeonfun/aeon PRs #890-#925 into the in-repo docs. Source of truth = merged PRs; this is the downstream propagation. (#888/#889 skipped: prior run's own sync artifacts.)

16 signal, 18 noise. No catalog change (still 75 skills).

Surfaces touched

• CHANGELOG.md - Unreleased Added/Changed/Fixed entries for every signal PR:
  • Added: Codex plugin + repo llms.txt (feat: Codex plugin + repo llms.txt #919), harnesses.json manifest (feat(harness-adapter): generated capability manifest (harnesses.json) #916), chain verdict routing (feat(chains): verdict routing on Haiku scores (when: on chain steps) #911), dry-run gate (feat(dry-run): gate self-authored skills before auto-merge #914), audit log (feat(audit): structured audit log of privileged actions #908), reactive handler var (feat(scheduler): reactive handler learns which skill tripped it (item 3) #910), validate-config reactive checks (feat(validate-config): validate reactive-trigger references and conditions #907), aeon-update 3-way merge (feat(aeon-update): 3-way merge OWNED conflicts + eyebrow-lock fail-safe #903), vuln-scanner A3.6 (feat(vuln-scanner): add A3.6 agentic logic audit alongside the fuzz pass #894), vuln-scanner deliverability gate (feat(vuln-scanner): DoH MX/A deliverability gate before autonomous disclosure email #895).
  • Changed: single-classic-PAT GH_GLOBAL model (docs: single classic PAT (repo+workflow) for GH_GLOBAL #905), README onboarding/harness section (docs(readme): agent-onboarding callout + harness section + asset optimization #922), security hardening (fix(security): narrow messages.yml ALL_SECRETS to named allowlist #904/security: SHA-pin all GitHub Actions to immutable commit refs #917/security: block codex install scripts + SHA256-pin eyebrow download #918), one Maintenance line for the rest.
  • Fixed: reactive success_rate (fix(scheduler): make reactive success_rate condition actually fire #906), bd-radar/fleet-control GH_GLOBAL fallback (fix(bd-radar,fleet-control): GH_GLOBAL fallback for private reads + silence false unset-GH_READ_PAT alarms #909), scorer full-output grade (fix(scorer): grade full output, align to strategy, flag fabrication #921), vuln-tracker/scanner ports (fix(vuln-tracker,vuln-scanner): port scan-history, PR-match, and osv-scanner robustness from aeon-vuln #890).
• plugin/skills/aeon/references/secrets.md - re-synced from the upstream setup skill. docs: single classic PAT (repo+workflow) for GH_GLOBAL #905 updated .claude/skills/aeon/references/secrets.md but not this byte-for-byte plugin copy, so it was left on the stale fine-grained token model. Now byte-equal to upstream (plugin transform holds: 5 CLAUDE_PLUGIN_ROOT lines, 0 stale paths).
• docs/aeon-setup.md - Option B now documents the Codex plugin install path (codex plugin marketplace add / codex plugin add) shipped by feat: Codex plugin + repo llms.txt #919, which touched only the manifests.

Noise bundled (Maintenance / Security)

#891, #892, #893 (model pins), #896, #897 (CI/model-pin doc), #898, #899, #900, #901, #902 (ops guards/timeouts), #904, #917, #918 (security hardening), #915 (apt bound), #920 (dashboard layout), #923, #924, #925 (README harness-section iterations).

Watermark moves 887 -> 925.