Feat v0.6.14 visual polish

Fix v0.6.13 spacing regressions with half-step tokens (--sp-1h 6px,
--sp-2h 10px). Purge ~65 stale hex/rgba fallback values from var() calls
including all old gold #b38a4e references. Self-host DM Sans and JetBrains
Mono woff2 fonts, eliminating Google Fonts CDN dependency. Standardize
border-radius to three tokens (--radius-sm 4px, --radius 8px, --radius-lg
12px) across all kernel CSS and 12 extension packages.

Also fixes: theme settings showing resolved mode instead of stored preference,
surface-inner overflow causing notes scrollbar and chat input clipping at
high zoom, user menu drift at scale >100% from zoom-unaware fixed positioning,
and three undefined CSS variable references.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/EXTENSION-CSS.md

@@ -122,7 +122,9 @@ values are acceptable.
 | Variable | Value | Computed |
 |----------|-------|---------|
 | `--sp-1` | `0.25rem` | 4px |
+| `--sp-1h` | `0.375rem` | 6px |
 | `--sp-2` | `0.5rem` | 8px |
+| `--sp-2h` | `0.625rem` | 10px |
 | `--sp-3` | `0.75rem` | 12px |
 | `--sp-4` | `1rem` | 16px |
 | `--sp-5` | `1.25rem` | 20px |
@@ -147,8 +149,9 @@ Example:
 |----------|---------|
 | `--font` | Primary font family |
 | `--mono` | Monospace font family |
-| `--radius` | Default border-radius (8px) |
-| `--radius-lg` | Large border-radius (12px) |
+| `--radius-sm` | Small border-radius (4px) — badges, inline controls |
+| `--radius` | Default border-radius (8px) — buttons, inputs, cards |
+| `--radius-lg` | Large border-radius (12px) — modals, dialogs, large cards |
 | `--transition` | Default transition timing |
 | `--shadow-lg` | Large elevation shadow |
 | `--overlay` | Modal overlay color |