Initial commit: Share-as-QR Firefox extension with bun build

MV3 WebExtension that turns the active tab's URL into a scannable QR
code via a toolbar popup. The popup runs locally — no network requests.

Build pipeline: `bun build` bundles popup.js + the vendored
kazuhikoarase/qrcode-generator (MIT, pinned to 83b7e8f) into a single
~23 KB minified ESM file under dist/. web-ext operates on dist/, so
the packaged zip contains only what actually ships (~28 KB).

Scripts:
- bun run build    — bundle + copy assets into dist/
- bun run lint     — build + web-ext lint (0 errors / 0 warnings)
- bun run package  — build + produce a signable .zip
- bun run start    — build + launch Firefox with the extension loaded

Tracks dogcat epic firefox-share-as-qr-35mw and its 5 child tasks
(scaffold, vendor lib, popup UI, icons, README).

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

package.json

@@ -0,0 +1,12 @@
+{
+  "name": "share-as-qr",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Firefox extension: share the current tab's URL as a QR code.",
+  "scripts": {
+    "build": "bun run scripts/build.mjs",
+    "lint": "bun run build && bunx --bun web-ext lint",
+    "package": "bun run build && bunx --bun web-ext build --overwrite-dest",
+    "start": "bun run build && bunx --bun web-ext run"
+  }
+}