fix(frontend): cyrillic glyphs for nav and section labels

The legacy ``@fontsource/geist-sans`` (v5.2.5) ships latin only and
``@fontsource/geist-mono`` was imported with the default subset only —
so Russian text in the sidebar (nav links, section labels, badges) fell
back to system fonts (Segoe UI / Cascadia / Consolas) and visibly
clashed with the Latin glyphs around it.

- Switched the sans family to ``@fontsource-variable/geist`` (single
  variable woff2 with latin + latin-ext + cyrillic). Updated
  ``--font-sans`` to lead with ``'Geist Variable'`` then keep the old
  ``'Geist Sans'`` and system fallbacks for safety.
- Added ``@fontsource/geist-mono/cyrillic-{400,500,600}.css`` imports
  so Geist Mono renders Russian glyphs in the section labels and
  monospace badges instead of falling back.

Newsreader (display serif) still has no Cyrillic on fontsource, so
italic page-hero emphasis in Russian still falls back to Georgia.
That's a separate, less-prominent concern and a future swap.

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
 	"name": "notify-bridge-frontend",
-	"version": "0.6.1",
+	"version": "0.7.0",
 	"lockfileVersion": 2,
 	"requires": true,
 	"packages": {
 		"": {
 			"name": "notify-bridge-frontend",
-			"version": "0.6.1",
+			"version": "0.7.0",
 			"dependencies": {
 				"@codemirror/autocomplete": "^6.18.0",
 				"@codemirror/lang-html": "^6.4.11",
@@ -14,6 +14,7 @@
 				"@codemirror/state": "^6.6.0",
 				"@codemirror/theme-one-dark": "^6.1.3",
 				"@codemirror/view": "^6.40.0",
+				"@fontsource-variable/geist": "^5.2.8",
 				"@fontsource/dm-sans": "^5.2.8",
 				"@fontsource/geist-mono": "^5.2.7",
 				"@fontsource/geist-sans": "^5.2.5",
@@ -607,6 +608,14 @@
 			"integrity": "sha512-RiB/yIh78pcIxl6lLMG0CgBXAZ2Y0eVHqMPYugu+9U0AeT6YBeiJpf7lbdJNIugFP5SIjwNRgo4DhR1Qxi26Gg==",
 			"dev": true
 		},
+		"node_modules/@fontsource-variable/geist": {
+			"version": "5.2.8",
+			"resolved": "https://registry.npmjs.org/@fontsource-variable/geist/-/geist-5.2.8.tgz",
+			"integrity": "sha512-cJ6m9e+8MQ5dCYJsLylfZrgBh6KkG4bOLckB35Tr9J/EqdkEM6QllH5PxqP1dhTvFup+HtMRPuz9xOjxXJggxw==",
+			"funding": {
+				"url": "https://github.com/sponsors/ayuhito"
+			}
+		},
 		"node_modules/@fontsource/dm-sans": {
 			"version": "5.2.8",
 			"resolved": "https://registry.npmjs.org/@fontsource/dm-sans/-/dm-sans-5.2.8.tgz",
@@ -2887,6 +2896,11 @@
 			"integrity": "sha512-RiB/yIh78pcIxl6lLMG0CgBXAZ2Y0eVHqMPYugu+9U0AeT6YBeiJpf7lbdJNIugFP5SIjwNRgo4DhR1Qxi26Gg==",
 			"dev": true
 		},
+		"@fontsource-variable/geist": {
+			"version": "5.2.8",
+			"resolved": "https://registry.npmjs.org/@fontsource-variable/geist/-/geist-5.2.8.tgz",
+			"integrity": "sha512-cJ6m9e+8MQ5dCYJsLylfZrgBh6KkG4bOLckB35Tr9J/EqdkEM6QllH5PxqP1dhTvFup+HtMRPuz9xOjxXJggxw=="
+		},
 		"@fontsource/dm-sans": {
 			"version": "5.2.8",
 			"resolved": "https://registry.npmjs.org/@fontsource/dm-sans/-/dm-sans-5.2.8.tgz",