Migrate Chrome and Edge builds to Manifest V3

[rthaut]

Migrates the Chrome and Edge builds to Manifest V3 ahead of the Chrome Web Store's MV2 removal deadline. Firefox continues to build MV2 with its existing 62.0 minimum. Closes #243.

What changed

• package.json: the chrome/edge build/zip/start scripts (and the default dev/build scripts, which target Chrome) no longer pass --mv2, so WXT builds MV3 for those targets. The firefox scripts keep --mv2.
• wxt.config.ts: the manifest now branches on manifestVersion:
  • page_action → action (MV3 has no page action)
  • the *://*.deviantart.com/* match pattern moves from permissions to host_permissions
  • web_accessible_resources uses the MV3 object format, scoped to *://*.deviantart.com/*
  • minimum_chrome_version becomes 88.0 (the MV3 floor) for both Chrome and Edge
• app/entrypoints/background.js: persistent is now MV2-only (MV3 runs as a service worker); the click listener binds to browser.pageAction ?? browser.action.
• app/scripts/background/tabs.js: page-action behavior is emulated on MV3 — the action button is disabled globally on install/startup and enabled per-tab when the tab is on deviantart.com. The button is therefore always visible in the toolbar (an MV3 constraint) but greyed out/non-clickable off-domain. Firefox still uses the real pageAction API (capability-checked, not browser-sniffed).
• app/scripts/background/runtime.js: browser.extension.getURL() (removed in MV3) → browser.runtime.getURL().
• scripts/smoke-manifests.js: now asserts the chrome-mv3/edge-mv3 outputs have the correct MV3 shape (service worker, action, host_permissions, object-format WAR, min version 88) while firefox remains MV2 with all of its existing checks.
• wxt.config.ts (second commit): explicit per-browser esbuild targets. Vite ignores browserslist, and the firefox bundle was shipping untranspiled ?./??/??= — syntax Firefox 62 (the declared strict_min_version) does not support. The firefox build now targets firefox62 and the Chrome/Edge builds target chrome88; the rebuilt firefox bundle contains none of those tokens.

No version bump here — versioning is handled by the pending release PR (#241).

Chrome manifest: MV2 → MV3 diff

--- chrome-mv2/manifest.json
+++ chrome-mv3/manifest.json
@@ -1,5 +1,5 @@
 {
-  "manifest_version": 2,
+  "manifest_version": 3,
   "name": "__MSG_ExtensionName__",
   "description": "__MSG_ExtensionDescription__",
   "version": "6.2.2",
@@ -17,7 +17,7 @@
   },
   "default_locale": "en",
   "homepage_url": "https://rthaut.github.io/deviantART-Filter",
-  "page_action": {
+  "action": {
     "default_icon": {
       "16": "images/icon-16.png",
       "19": "images/icon-19.png",
@@ -36,18 +36,24 @@
     "contextMenus",
     "notifications",
     "storage",
-    "tabs",
+    "tabs"
+  ],
+  "host_permissions": [
     "*://*.deviantart.com/*"
   ],
   "web_accessible_resources": [
-    "create-filters.html"
+    {
+      "resources": [
+        "create-filters.html"
+      ],
+      "matches": [
+        "*://*.deviantart.com/*"
+      ]
+    }
   ],
-  "minimum_chrome_version": "49.0",
+  "minimum_chrome_version": "88.0",
   "background": {
-    "persistent": true,
-    "scripts": [
-      "background.js"
-    ]
+    "service_worker": "background.js"
   },
   "content_scripts": [
     {

(The icons, content_scripts, name/description/locale, and permissions other than the host pattern are unchanged. The edge-mv3 manifest has the same shape.)

Validation

npm test passes end-to-end (exit 0):

• eslint ./app/ — 0 problems
• wxt build for chrome (MV3), edge (MV3), firefox (MV2)
• manifest smoke tests — Validated chrome manifest (MV3), Validated edge manifest (MV3), Validated firefox manifest (MV2)
• wxt zip for all three targets
• web-ext lint on the firefox build — 0 errors, 0 notices, 6 pre-existing warnings (eval/innerHTML flags from bundled third-party libraries)

Transpilation check: scanning the built firefox bundle for ?. / ?? / ??= finds none after the firefox62 target (all three appeared throughout the bundle before it).

Manual test checklist (Chrome, unpacked .output/chrome-mv3)

• Extension loads with no errors on chrome://extensions (service worker starts; no MV2 deprecation warning)
• Toolbar button is present but disabled (greyed out, not clickable) on non-DeviantArt tabs
• Toolbar button becomes enabled on a deviantart.com tab, and clicking it opens (or focuses) the Manage page
• Filters apply on browse/search pages (existing user/keyword filters hide deviations)
• Creating a filter from the Manage page works and takes effect on an open DeviantArt tab without a reload
• The create-filters page opens from a deviation (web-accessible resource loads)
• Right-click context menus on tag/deviation links appear and create filters
• After restarting the browser, the button is disabled off-domain and re-enables on deviantart.com tabs
• Quick smoke of the unpacked .output/edge-mv3 build in Edge (button behavior + filtering)
• Firefox regression check (.output/firefox-mv2): page action still appears in the address bar on deviantart.com only, and filtering works