Fix the finish review's 8 material findings on the teletext redesign

Applies the fix round from the finish-reviewer's disposition on commit
4b19cbd, in one batch:

- System's disk table is unreadable below 560px: horizontal-scrolling a
  6-column table hid the usage bar and the temperature, the two
  readings that matter most (discipline 3 — one shared ruler — was
  unauditable as a result). Added a disk_row() macro and a phone-only
  .tt-disk-rows reflow (name + full 20-cell bar + temp on one line,
  device/free/total beneath), CSS-toggled against the existing table
  at the same breakpoint.
- Contrast failure on the highest-severity state: white text on the
  red .tt-field.crit/.tt-toast.error/.tt-btn.armed reversals measured
  4.0:1, under the 4.5:1 floor. Switched to black text (5.25:1),
  matching the black-on-yellow .warn pattern already in use — and
  fixed a second instance of the same bug: .tt-field.crit had no
  .tt-field-meta override, unlike .warn.
- Two type families where the direction contract names one blocky
  monospace: unified on a single self-hosted face (Space Mono, one
  weight, no bold) for both body and the double-height row.
- FIRST VIEWPORT proportion: an unpromised 6-item Just Added grid was
  competing with NOW SHOWING for the fold instead of the contract's
  "lower two-thirds in double-height cyan." Cut to a fixed 3-item,
  fixed-3-column row, which also fixes the orphaned-tile grid defect
  as a side effect (a fixed count can't leave a lone tile beside empty
  tracks).
- Three flat mid-grey fills contradicted discipline 1 (no in-between
  tone): .tt-tile-art, .tt-btn:disabled, and .tt-err pre all painted a
  solid --ink-dimmer background. Centralized the dither .tt-tile-art
  already used correctly into a shared --dither-mid generator and
  applied it to all three.
- Google Fonts dependency on a LAN-only home server: a dropped webfont
  request was a silent identity change, not a graceful fallback.
  Self-hosted Space Mono under static/fonts/ via @font-face; dropped
  the <link> tags from _shell.html and login.html.
- Deliberately deferred: "pages differ in stock" (discipline 5) still
  fires on only one band service-wide. Every other finding was a
  bounded fix to existing code; this one asks for a new mechanism (an
  aggregate status band on P100) rather than a correction, so it's
  flagged for a follow-up rather than rushed into this batch.

Recaptured desktop.png, mobile.png, desktop-system.png and
mobile-system.png (the four files the reviewer's findings cited)
through the same true-390px iframe method as the prior round, and
returned them for the fix round's verdict pass.

Known follow-up: DESIGN.md's typography section (written by the
documenter before this batch) still names the old two-family pairing
and needs a re-run now that the font system changed under it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NBw1QodG8ZMYHrGeQfqyDS

static/css/base.css

@@ -29,6 +29,23 @@
       pages is a failure.
    ═══════════════════════════════════════════════════════ */
 
+/* Self-hosted, deliberately: this app runs on a LAN-only home server
+   behind a filtered/offline-capable network, where a Google Fonts
+   request can simply fail. A dropped @font-face request means every
+   character on the page silently falls back to whatever monospace the
+   OS ships — a different world by accident, not a variation of this
+   one. One weight only (400): there is no bold in this system. */
+@font-face {
+  font-family: 'Space Mono';
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url('../fonts/SpaceMono-Regular.woff2') format('woff2');
+  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6,
+    U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122,
+    U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
 :root {
   /* ── The locked eight ──────────────────────────────────
      Teletext had exactly these, at full saturation, and the
@@ -67,18 +84,28 @@
   --ink-dim:    color-mix(in srgb, var(--tt-white) 58%, var(--tt-black));
   --ink-dimmer: color-mix(in srgb, var(--tt-white) 30%, var(--tt-black));
 
+  /* The one legal way to fill an area with a mid-tone: every "flat
+     grey panel" in the codebase (a disabled button, an unloaded poster,
+     a code block behind an error detail) draws from this generator
+     rather than declaring --ink-dimmer as a solid background. A solid
+     fill of a dimmed token is still a ninth colour by another name. */
+  --dither-mid: repeating-linear-gradient(45deg,
+    var(--ink-dimmer) 0 1px, var(--tt-black) 1px calc(var(--dither-size) * 2));
+
   /* ── Type: one face, exactly two heights ───────────────
-     Teletext's entire scale. Emphasis comes from colour and
-     from doubling the height, never from a weight ramp and
-     never from a third size. */
+     Teletext's entire scale — ONE family, not one for body and a
+     different one for the double-height row. Emphasis comes from
+     colour and from doubling the height, never from a weight ramp
+     (this face loads a single weight, 400, on purpose — there is
+     no bold anywhere to reach for) and never from a third size. */
   --fs:   0.9375rem;  /* 15px — the single body size */
   --fs2:  1.875rem;   /* 30px — double height, the only other size */
   --lh:   1.45;
   --row:  calc(var(--fs) * var(--lh));   /* one character row */
   --cell: 1ch;
 
-  --font:    'Chivo Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
-  --font-dh: 'DotGothic16', 'Chivo Mono', ui-monospace, Menlo, monospace;
+  --font:    'Space Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  --font-dh: var(--font);
 
   /* ── Measure ───────────────────────────────────────────
      A teletext page was 40 columns. A screen this wide gets