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

tools/mkcapsule.c

@@ -740,11 +740,6 @@ static int cmp_blockref(const void *a, const void *b) {
 }
 
 static void generate_manifest(FILE *out) {
-    time_t now = time(NULL);
-    struct tm *tm_ptr = gmtime(&now);
-    char timestamp[64];
-    strftime(timestamp, sizeof(timestamp), "%Y-%m-%dT%H:%M:%SZ", tm_ptr);
-
     qsort(manifest_entries, (size_t)manifest_count,
           sizeof(ManifestEntry), cmp_manifest_name);
 
@@ -762,11 +757,11 @@ static void generate_manifest(FILE *out) {
 
     fprintf(out,
         "# Capsule Block Manifest — Auto-generated\n"
-        "<!-- Generated by mkcapsule --manifest  %s -->\n"
+        "<!-- Generated by mkcapsule --manifest (no timestamp: it changes only with the capsules) -->\n"
         "<!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->\n"
         "<!-- Hand-written justifications and immutability notes live  -->\n"
         "<!-- in MANIFEST.md alongside this auto-generated index.      -->\n"
-        "\n", timestamp);
+        "\n");
 
     /* Capsule summary */
     fprintf(out, "## Capsule Summary\n\n");