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

capsules/BLOCK_MAP.md

@@ -1,5 +1,5 @@
 # Capsule Block Manifest — Auto-generated
-<!-- Generated by mkcapsule --manifest  2026-10-17T02:58:45Z -->
+<!-- Generated by mkcapsule --manifest (no timestamp: it changes only with the capsules) -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
 <!-- in MANIFEST.md alongside this auto-generated index.      -->