fix: seat the build stamp in #120's redesigned bar, and stop it faking a ticket id

Three things the merge with #120 (ui/shell-polish) actually required, none of
which a clean auto-merge could have told us.

MOVED, not preserved. #120 left <header>'s markup alone but gave every child
explicit styling and a stated reading order -- "what this is, which document,
which view, which mode, what keys, what the peer is doing". A build identifier
is "what this is", so the span moves from after #status to beside <h1>. Keeping
it at the tail was loyalty to my own first draft: it read as metadata trailing
#status, and with #hint's `flex: 1 1 auto` fighting for the slack a 40-char
commit SHA there is the thing that crowds the bar.

STYLED, because unstyled is illegible-by-default in a design system. It takes
`var(--dim)` -- the same token #hint and #status use, so it tracks both themes
by construction rather than by a hand-picked colour -- at 0.72rem, and clamps
to 14ch. Measured under Chromium on the merged tree: a tag renders whole
(scrollWidth == clientWidth, 69px), a 40-char SHA truncates to a 13-character
prefix with an ellipsis, and `header` does not overflow in either case
(scrollWidth == clientWidth == 1280). Contrast of rgb(107,103,95) on
rgb(244,241,234) is ~5.0:1, above AA for small text. Selecting the text still
copies the whole SHA -- text-overflow is a rendering clamp, not a truncation.

NOT AN ID. `improvise-web.tar.gz` puts the token `improvise-web` in the tree,
and AGENTS.md's audit matches `improvise-[a-z0-9]{3,8}` -- so the artifact name
resolved to no ticket and read exactly like a dead id, which AGENTS.md calls
worse than one. `improvise-installer.sh` escapes only by being ten characters,
which is luck rather than a rule, so the exclusion list gains `web` and the
paragraph gains the general case.

RELEASING.md (which arrived in this same merge, from improvise-gx5d) listed
what a tag publishes and was made wrong by omission; it now names the web
capture and says plainly that it is not what Pages is serving.

Verified on the merged tree: 1631 cargo tests over 37 binaries, node --test
47 -> 50 (so #120's three new shell tests survived the merge rather than being
silently dropped), 42 Playwright tests green under Chromium, and the stamp
gate re-proved by injecting the missed substitution again -- a header rewrite
does not carry the old fault injection.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FC2jVn8Au7E9JPkw6bwXXH

web/style.css

@@ -87,6 +87,20 @@ header h1 {
   flex: none;
 }
 
+/* Which build this is (improvise-oujb). Quietest thing on the bar -- it is
+   reference, never state -- but it must stay legible enough to quote. */
+#build-version {
+  flex: none;
+  /* A tag fits whole; a 40-char commit SHA truncates to a prefix long enough
+     to name a build, and selecting the text still copies the whole thing. */
+  max-width: 14ch;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  color: var(--dim);
+  font-size: 0.72rem;
+}
+
 #doc-name {
   flex: none;
   /* Wide enough for the shipped document's whole title, `name (stored_as)`,