design: bundle Inter + JetBrains Mono (OFL-1.1) as the standard typefaces

The DESIGN.md type standard needs the fonts actually present — the machine's installed faces
are not a design system. Four Inter weights (400/500/600/700) and two JetBrains Mono weights
(500/600) ship as WPF resources from Assets/Fonts; the token families resolve them with the
`/Assets/Fonts/#Family` pack form, so nothing depends on an install or a network fetch.

Licensing (recorded in docs/ai/product.md): OFL-1.1 is a free licence but is NOT GPL-compatible
in the linking sense. These are separate .ttf files loaded through WPF's font stack — an
aggregate, not linked code — so they coexist with the GPL-3.0 app. Obligations carried:
copyright line in THIRD-PARTY-NOTICES.txt (new items 13-14), the OFL text beside the files
(Assets/Fonts/OFL-*.txt), no modification, no reserved-name reuse.

Guard: BundledFontsTests — files exist and are real binaries, the csproj ships them, the theme
uses pack URIs (a bare family name would silently fall back), the notice and both OFL texts are
present, and no third font family sneaks in.

Pending visual confirmation: the first launch should render panel text in Inter and telemetry
in JetBrains Mono.

DESIGN.md

@@ -177,5 +177,5 @@ rejected in favour of the values above.
 - **Still to sweep:** `Themes/Controls.xaml` and the dozens of hardcoded hexes in XAML/C# still use
   the legacy palette. Surfaces convert one at a time; the end state is that every colour, radius and
   spacing value resolves from `Tokens.xaml` and a guard fails on any raw `#hex` outside it.
-- Fonts (Inter, JetBrains Mono) are declared as token families with system fallbacks; the bundled
-  font assets land next.
+- **Fonts ship with the app** (`Assets/Fonts/*.ttf`, OFL-1.1) — no installation, no network, no
+  dependence on what the machine happens to have. Notice and license text travel with them (`THIRD-PARTY-NOTICES.txt` items 13-14).