v0.1.2: rebrand to Naiv-QR, target AMO-listed distribution

Pre-AMO rename. The extension is now "Naiv-QR" everywhere it surfaces
to users (toolbar tooltip, popup title, icon aria-label, README,
package.json). Distribution target is AMO-listed, so the manifest no
longer declares gecko.update_url — Firefox handles auto-updates from
AMO directly for listed extensions, and the field is in fact rejected
by Mozilla's validator outside self-distribution mode.

- manifest.json: name → "Naiv-QR"; gecko.id → naiv-qr@addons.naiv.no;
  remove update_url.
- package.json: name → "naiv-qr"; drop --self-hosted from lint script
  now that we're back to Mozilla-hosted validation.
- popup/popup.html: <title> updated.
- icons/icon.svg: aria-label updated.
- README: retitled, removed Self-distribution section, updated
  Publishing-to-AMO section to spell out the listed-distribution flow.

Build artifact is now web-ext-artifacts/naiv-qr-<ver>.zip (web-ext
derives the filename from manifest.name).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

icons/icon.svg

@@ -1,4 +1,4 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" role="img" aria-label="Share as QR">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" role="img" aria-label="Naiv-QR">
   <rect width="32" height="32" rx="6" fill="#1f2937"/>
   <g fill="#f9fafb">
     <!-- Top-left finder -->