ui: sidebar tab selector uses text labels instead of icons

The two drawn tab glyphs were judged not understandable enough; the
switcher goes to the wide policy with titles only, and the glyphs,
their gresource entries and the icon-naming code are removed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/verification.md

@@ -17,8 +17,8 @@ Two baselines every run is read against. The UDPS runs must be **unchanged by th
 a UDPS self-check, number-normalised (`sed 's/[0-9.]\+/N/g'`), diffs empty against one taken before it.
 A clean build emits **three** warnings and no more: two
 `-Wmissing-field-initializers` on `MathNode::source` and one `-Woverlength-strings` on the icons'
-generated GResource `.c`, whose blob is **12352** against C99's 4095-byte string-literal limit with
-the seven action icons and the two app icons that remain (a note about a generated file, which GCC
+generated GResource `.c`, whose blob is **9248** against C99's 4095-byte string-literal limit with
+the five action icons and the two app icons that remain (a note about a generated file, which GCC
 itself supports). The *fourth* was the help pages' generated `.c` (**516044** bytes); the manual is
 now a Mallard set installed for Yelp rather than a GResource compiled into the binary, so that
 bundle — and its warning — is gone, and the baseline moved from four to **three**. Re-measure by