Keep extension zips out of the repo — make prod builds them ...

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

Download page: extension install guide for Chrome and Firefox ...

- public /download page (nav item «Расширение»): per-browser download
  buttons and step-by-step install instructions, setup (server URL is
  the panel's own origin) and hotkey reference, en/ru
- npm run package -w @ltt/extension zips dist/{chrome,firefox} into
  packages/web/public/ext (stable names, manifest at archive root so
  "Load unpacked" works right after unpacking)
- make ext / make prod always build fresh zips; deploy/.env.example
  seeds the release address bugtrail.gnexus.space

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

Add BugTrail logo: extension icons, favicons and popup/options branding ...

SVG mark (brand/bugtrail.svg): a bug at the head of the trail of steps
it walked, Tokyo Night palette. PNG icons 16/32/48/128 are rendered
from it (verify-logo.mjs) and shipped in the extension manifest;
web panel gets an SVG favicon; popup and options headers show the mark
instead of the generic bug glyph.

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