SPEC §2.4: allow factual comparisons, never with Stalwart

The last bullet forbade comparison of any kind. Public material may now
compare inbuxa with the hosted suites organizations choose between and
with other self-hosted mail stacks, when the comparison is factual,
dated, names no price and says when the other choice is better.
Stalwart is still never compared: no editions, no pricing, no
commentary on Stalwart Labs or other forks.

The lineage is now told in the past tense ("started as a fork of
Stalwart"), once, with the clean-room provenance on one documentation
page that everything else links to.

docs/spec/SPEC.md

@@ -209,9 +209,9 @@ depends on `store` and can't be called from it (`features/scale-out-storage.md`)
 
 - No "Stalwart" in product names, binaries, images, UI text, packaging or
   domains.
-- Factual statements are allowed and required: "a fork of Stalwart",
-  "compatible with Stalwart 0.16 data". Upstream copyright notices stay on
-  every file they cover.
+- Factual statements are allowed and required: "started as a fork of
+  Stalwart", "compatible with Stalwart 0.16 data". Upstream copyright notices
+  stay on every file they cover.
 - **Identifiers people meet carry the fork's name** (changed 2026-09-22;
   this bullet used to keep upstream's). Upstream's JMAP capability for the
   registry (`x:`) objects is `urn:inbuxa:jmap:registry`, beside the fork's
@@ -242,14 +242,25 @@ depends on `store` and can't be called from it (`features/scale-out-storage.md`)
 - **Public material names it once, as fact, with the mark attributed** (added
   2026-09-19). Where the name appears outside the product — the site, release
   announcements, documentation — it carries the attribution: Stalwart is a
-  trademark of Stalwart Labs LLC, and INBUXA is not affiliated with or
-  endorsed by them. The fork relationship is stated in the provenance or
-  license section, and the migration path names the server it migrates from,
-  because an operator searching for it has to find it. The base *version*
-  belongs with the operator-facing material above — not in taglines, page
-  titles, hero copy or social previews, where it reads as a source identifier
-  rather than a fact. No comparison, favorable or otherwise: what INBUXA
-  offers is stated on its own terms.
+  trademark of Stalwart Labs LLC, and inbuxa is not affiliated with or
+  endorsed by them. The lineage is told in the past tense: inbuxa *started as*
+  a fork of Stalwart and its server *descends from* it; never "built on
+  Stalwart" or "Stalwart with extras". It is told once, in the license or
+  about section, and the clean-room provenance lives on one documentation
+  page that everything else links to. The migration path names the server it
+  migrates from, because an operator searching for it has to find it. The
+  base *version* belongs with the operator-facing material above — not in
+  taglines, page titles, hero copy or social previews, where it reads as a
+  source identifier rather than a fact.
+- **Comparisons: other products yes, Stalwart no** (changed 2026-10-05; this
+  bullet used to forbid comparison of any kind). Public material may compare
+  inbuxa with the hosted suites organizations choose between and with other
+  self-hosted mail stacks, when the comparison is factual, dated, names no
+  price, and says when the other choice is the better one. Self-hosted peers
+  are treated with respect. Stalwart is never compared: no editions, no
+  pricing, no commentary on Stalwart Labs or other forks. The rebuilt features
+  are described on their own merits, never as the features someone else
+  charges for.
 
 ### 2.5 Packaging