cc-sidepanel: bundle JetBrainsMono Nerd Font Mono (0.3.0)

The panel should match kitty's font, but extension pages can't reach system
fonts by name — CSP blocks `local()` — so the TTFs ship in the repo:

  fonts/JBMono-Regular.ttf  2.5MB  weight 400
  fonts/JBMono-Bold.ttf     2.5MB  weight 700

Copied from /usr/share/fonts/TTF/JetBrainsMonoNerdFontMono-{Regular,Bold}.ttf.
Heavy, but it's local-only — the panel never downloads them.

`@font-face` in sidepanel.html, fallback chain kept (ui-monospace, SF Mono,
Menlo, monospace). Line-height 1.4 -> 1.5 for JBMono's taller glyphs.

The Nerd Font variant means nerd-font glyphs leaking out of the pane render
properly instead of as boxes.

No `web_accessible_resources` needed: the side panel is an extension page on the
same chrome-extension:// origin, so bundled files are directly reachable. That
key is only for files injected into web pages.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

extension/manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "CC Sidepanel",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "Live window into a Claude Code seat, right in the browser sidebar.",
   "icons": {
     "16": "icons/icon16.png",