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/index.html

@@ -34,17 +34,18 @@
     -->
     <header>
       <h1>improvise</h1>
+      <!--
+        What this page IS: web/assemble.sh rewrites the text below to the tag
+        or commit it assembled from (improvise-oujb). It sits with the name
+        because the bar's order starts at "what this is", and a tree served
+        straight out of web/ was never assembled and honestly says so.
+      -->
+      <span title="Build this page was assembled from" id="build-version">unstamped</span>
       <span id="doc-name"></span>
       <span id="view-name"></span>
       <span id="mode"></span>
       <span id="hint"></span>
       <span id="status" role="status"></span>
-      <!--
-        What this page IS: web/assemble.sh rewrites the text below to the tag
-        or commit it assembled from (improvise-oujb). A page served straight
-        out of web/ was never assembled and honestly says so.
-      -->
-      <span title="Build this page was assembled from" id="build-version">unstamped</span>
     </header>
 
     <!--