web: give display text an optical size using Inter's opsz axis

[mforce]

Component plan: build this from the components named in docs/designs/822-mui-revamp.md. The rule is "reused, never rebuilt" — composing MUI primitives into a screen wrapper is expected; reimplementing behaviour a shared component already has is not. Say in the PR which row of that table covers this screen.

Part of #674. Inherited from #656 (closed 2026-09-13), question 2 of 3.

Inter everywhere at one optical size gives headings and stat figures no voice.
font-variation-settings: "opsz" 32 on h1, h2, .stat-value buys tighter display cuts at zero
download cost.

Already answered, incidentally (2026-09-02): the installed @fontsource-variable/inter does
carry the opsz axis — web/node_modules/@fontsource-variable/inter/files/ contains
inter-*-opsz-normal.woff2. The risk that the default entry ships wght only does not apply.
Do not re-investigate this.

Interacts with the MUI typography scale decision on this epic — if MUI owns headings after
conversion, this setting has to reach MUI's Typography too, not only bare h1/h2.

[mforce]

Amendment (2026-09-14, from the #822 design doc, PR #862). The premise "the installed Inter does carry the opsz axis, zero download cost, do not re-investigate" is wrong in the way that matters: the files are in the package, but main.tsx imports the default entry whose seven url()s are all wght-only faces (grep -c opsz node_modules/@fontsource-variable/inter/index.css = 0). font-variation-settings: "opsz" on the loaded face does nothing. Adopting the axis means switching to the opsz.css entry, which costs +118.9 KiB of precache across the seven subsets (+24.1 KiB on the latin subset a phone fetches), charged against #825's ceiling. Design direction: D7.2 in docs/designs/822-mui-revamp.md.

[mforce]

Closed as not planned (owner decision, 2026-09-24). The display optical size change was judged not worth it: it affects six stat figures, and the visible difference is small. PR #948 closed unmerged.

[mforce]

Reopened: the close earlier today was a coordinator misreading. The owner meant to skip the screenshot preview, not the change. #835 continues in PR #948.