perf(web): read the font stack from one variable to halve the token cost

The 103-character app font stack was copied into every Material typography
token: 47 component tokens, the 30 new --mat-sys-* typescale tokens and the
typography hierarchy, 91 copies in all. Declare it once as
--app-font-family on html and pass var(--app-font-family) to the theme and
the hierarchy instead: -6,941 bytes of initial CSS (1,611,987 ->
1,605,046), so the system tokens now cost 5,671 bytes net instead of 12,526.
The rendered font is unchanged.

Lower the raised baseline to the new measurement. theme-tokens.e2e.ts
applies var(--mat-sys-label-small) and checks its family, size and weight,
because a dangling var() would void the whole font shorthand while body text
still inherited the same family.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/performance/journey-baselines.json

@@ -3,7 +3,7 @@
     "journeys": {
         "launch": {
             "renderer.initialBytes": {
-                "value": 1611987,
+                "value": 1605046,
                 "unit": "bytes",
                 "slack": 4096,
                 "updatedAt": "2026-10-01",