docs(v1.10.1): cut v1.10.1; v1.10.0 stays tagged-but-never-published

v1.10.0's build failed one assertion of 104 and published nothing. Rather than
re-point a tag CI had already consumed, the number moves: a version that failed
its build should stay failed and readable, not be quietly overwritten with
different bytes.

CHANGELOG gains a v1.10.1 section carrying the smoke fix (moved out of
v1.10.0's Fixed list), and states plainly that everything under v1.10.0 ships
here so the big section stays the content record. v1.10.0's heading is marked
"tagged, never published — superseded by v1.10.1" with a blockquote naming the
commit (12f99c4), the run (704), the four jobs that skipped, and the fact that
no image carries the tag.

Pre-tag doc sweep, because CI reads docs from the TAG and POSTs DOCKER_HUB.md
to the Hub as full_description:

  - README "Terminal UI mode: fullscreen is the default (since v1.10.0)"
    -> v1.10.1. A "since" marker pointing at an image nobody can pull is a
    worse lie than no marker.
  - Dockerfile.variant decision comments for the pi and pi-atelier bumps
    -> v1.10.1 (these describe which release carries the change).
  - scripts/smoke-test.sh deliberately KEEPS "the v1.10.0 tag build" — that
    one is a historical event and v1.10.0 is its correct name.
  - DOCKER_HUB.md needed no change: its fullscreen note is version-free.

No code changes. RELEASE_TAG is derived from github.ref_name, so nothing in the
build hardcodes the version.

Base layer does NOT rebuild: no base input (Dockerfile.base, rootfs/**,
entrypoint.sh, entrypoint-user.sh) has changed since 12f99c4, so base-decide
will cache-hit base-dad0f365ff24, which run 704's build-base already pushed at
07:52:38Z. This retry skips the expensive half.

Gates: doc-drift 23 OK / 0 DRIFT / 0 SKIP; base-hash, workflow-shell,
skill-floor, lint-shell all rc=0.

README.md

@@ -358,7 +358,7 @@ DOT syntax errors instead of crashing. Then in Studio: open the PNG (or a
 `.md` that embeds it) and hit **refresh-from-disk** after each edit.
 Note: SVG is **not** in Studio's local-image-link allowlist — use PNG.
 
-## Terminal UI mode: fullscreen is the default (since v1.10.0)
+## Terminal UI mode: fullscreen is the default (since v1.10.1)
 
 pi **1.0.0** changed the default terminal UI mode to **fullscreen**, and this
 image adopts upstream's default rather than overriding it. Fullscreen draws into