AGENTS.md: the versioning rule gains its major number

0.3.12's rule (§11) said the major number stays 0 and that what 1.0 would
mark is not decided. It is now: the major number moves when a release
changes what an installed phone does without being asked — not with an
ABI change (the ABI is frozen) and not with the size of a release. The
rule comes first so the commits that follow can name the release they are
part of.

AGENTS.md

@@ -1019,12 +1019,12 @@ only the imsd side of its bus choice.
   behaviour, in one sentence how it was tested. A version bump is a commit
   titled `imsd X.Y.Z` that changes only the `Version` constant and has no
   body.
-- **Versioning.** `0.MINOR.PATCH`: the patch number counts releases, fixes
-  and features alike; the minor number moves when a release changes what
-  a user can rely on the daemon for (0.3 added emergency calling), not
-  with the size of a release; the major number stays 0 — what 1.0 would
-  mark is not decided, and it is not an ABI change (§8.1: the ABI is
-  frozen).
+- **Versioning.** `MAJOR.MINOR.PATCH`: the patch number counts releases,
+  fixes and features alike; the minor number moves when a release changes
+  what a user can rely on the daemon for (0.3 added emergency calling), not
+  with the size of a release; the major number moves when a release changes
+  what an installed phone does without being asked, and it is not an ABI
+  change (§8.1: the ABI is frozen).
 - **No AI attribution trailers.** Commits carry no `Assisted-by:`,
   `Co-Authored-By:` or similar lines, whoever or whatever drafted them.
 - **Signed commits.** Every commit is GPG-signed with the repository's