fix(ui): meet 44px touch-target floor on shared mobile primitives

The desktop/mobile consistency review found primary mobile controls
rendering below the ~44px comfortable touch floor. Address the genuinely
shared primitives in one pass:

- Add a --tap-min: 44px token (documented anchor for the floor).
- tokens.css: text inputs, selects, and submit buttons grow to --tap-min
  under the 640px breakpoint (fixes the 36px auth/login form controls).
  Scoped to form controls + type=submit so dense icon buttons aren't
  inflated.
- SegmentedControl: .seg options reach the floor on mobile (it doubles as
  the catalog sort toggle and the Library tab switcher).
- Chip: expand .chip-remove's tappable area to --tap-min via a centered
  pseudo-element so the 16px glyph stays compact and tag rows don't grow.

Pure-CSS responsive change — jsdom can't evaluate @media or layout, so the
test pins the stylesheet contract (each shared primitive bumps to --tap-min
inside the mobile breakpoint), guarding against the bump being dropped.

The per-route .icon-btn (copy-pasted across seven files) is left for a
separate refactor.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1517,7 +1517,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.88.0"
+version = "0.88.1"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.88.0"
+version = "0.88.1"
 edition = "2021"
 default-run = "mangalord"