build: a build no longer dirties the tree

v3/include/version.h is written by every build (kernel/Makefile and
v3/Makefile, both FORCE), with a timestamp and the last build's ARCH; the
committed copy was stale (LITHOS_VERSION 2.1.0). Untracked, and .gitignore's
entry corrected: it said include/version.h, the path before the move to v3/,
and matched nothing.

capsules/BLOCK_MAP.md differed on every build only in mkcapsule's
"Generated ... <timestamp>" header. The timestamp is dropped, so the manifest
changes only when the capsules do; two runs are byte-identical.
mkcapsule's warnings unchanged (5, #143).

Captain Bob, 2026-11-11: untrack version.h and fix the ignore; drop the
manifest timestamp.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm

.gitignore

@@ -16,7 +16,8 @@ docs/api/
 *.iml
 
 # generated headers
-include/version.h
+# v3/include/version.h is written by every build (kernel/Makefile, v3/Makefile): untracked 2026-11-11
+v3/include/version.h
 
 # bundles / archives
 *.bundle