fix(seo): I1 — scope Off-page axis to what is actually measured

Axis was defined "backlinks, mentions, authority" (10% local / 15%
national of the FULL score) but only mentions have a data source
(STEP 6 web_search "<name>" -site:<domain>). Backlinks and authority
have no index, no API — the agent had to invent 2/3 of the number, and
that number reaches a client via /client-handover.

- Axis label names what is measured + points at §14.
- Off-page axis note: score mentions ONLY; never price in unmeasured
  sub-components; a low mention count is NOT evidence of a weak backlink
  profile. Mandatory verbatim §14 line naming the gap + the nearest free
  source (Common Crawl) so the omission is legible, not silent.
- LOCAL N/A label: was `N/A — requires FULL audit`, a promise FULL cannot
  keep for backlinks. Now states FULL covers brand mentions only.

Weights deliberately unchanged: re-deriving now and again when a backlink
source lands would churn historical scores twice. Revisit when the axis
widens back (Common Crawl, phase 5).

Note: initial plan was to mark the axis N/A in FULL and redistribute the
weight. Reading the real spec (seo-analyzer.md:622 + STEP 6) showed that
over-corrects — it discards the mentions data, which IS gathered. Narrowed
the definition instead; composes with the Common Crawl work later.

Verified: make test 35 GREEN / 0 RED.

agents/seo-analyzer.md

@@ -619,7 +619,7 @@ FIX: AUTO (<what agent will do>) | USER (<what user must do>)
 | Technical (perf, CWV, security headers, indexability) | 20% | 30% | |
 | On-page (content, meta, headings, images, video, a11y, i18n) | 20% | 30% | |
 | SEO Local (NAP, GMB, citations) | 25% | 5% | |
-| Off-page (backlinks, mentions, authority) | 10% | 15% | |
+| Off-page (unlinked brand mentions — backlinks/authority NOT auditable, §14) | 10% | 15% | |
 | Social presence | 10% | 5% | |
 | Competitive position | 5% | 10% | |
 | Legal compliance | 10% | 5% | |
@@ -628,6 +628,23 @@ FIX: AUTO (<what agent will do>) | USER (<what user must do>)
 real users, from STEP 4) when available; otherwise lab PageSpeed
 Lighthouse run.
 
+**Off-page axis note (I1).** Score ONLY the unlinked brand mentions
+gathered in STEP 6 (`web_search "<business-name>" -site:<domain>`).
+Backlink profile and domain authority have NO data source here — no index,
+no API, nothing. NEVER price them into the number: an unmeasured
+sub-component cannot be judged, and this axis carries 10-15% of a score
+that reaches a client via `/client-handover`. A low mention count is a low
+mention count — it is NOT evidence of a weak backlink profile.
+
+Mandatory §14 line whenever depth=FULL, verbatim:
+`Backlinks / domain authority — NOT audited: no backlink index wired.
+Nearest free source: Common Crawl hyperlinkgraph. Commercial: Ahrefs /
+Semrush / Majestic. The Off-page score above prices in brand mentions only.`
+
+Weight deliberately unchanged despite the narrower scope: re-deriving it
+now, then again when a backlink source lands, would churn historical
+scores twice. Revisit the 10/15% only when the axis widens back.
+
 ### LOCAL depth — 4 axes
 
 | Axis | Weight (local B2C) | Weight (SaaS/national/content) | Score /20 |
@@ -638,7 +655,11 @@ Lighthouse run.
 | Legal compliance (pages, CMP, mentions) | 20% | 15% | |
 
 LOCAL axes not audited (Off-page, Social, Competitive) appear as
-`N/A — requires FULL audit` in the report.
+`N/A — requires FULL audit` in the report. Off-page is the exception to
+that promise: FULL audits its brand-mentions share ONLY — backlinks and
+authority are unauditable at EVERY depth (see the Off-page axis note).
+Print `N/A — FULL audits brand mentions only` for it, never a bare
+"requires FULL audit" that FULL cannot keep.
 
 ### Projected code-only score + trajectory to 17/20 (mandatory)