test(extension): unit suite for lib/ + version-consistency specs

extension/ had no test harness at all -- web-ext lint was the only signal, so
the URL-normalization fix in 8214afe shipped with nothing exercising it.

Adds vitest (mirroring frontend/vitest.config.js) and three specs:

- url.spec.js       normalizeApiUrl / webRootFromApiUrl, including the #2393
                    regression: instance-root input must reach /api/credentials,
                    idempotence, trailing-slash and whitespace handling, and
                    that empty input never yields a bare "/api" (which
                    isConfigured() would read as configured).
- platforms.spec.js getPlatformFromUrl / isArtistPage, pinning the #1485
                    regression -- all three Patreon creator URL shapes
                    (bare, /c/, /cw/) plus inner pages, with nav pages
                    excluded -- and table-integrity checks.
- version.spec.js   manifest.json and package.json versions in lockstep,
                    AMO-safe version format, and url.js ordered before api.js
                    in background.scripts (classic scripts share one scope, so
                    a reorder is a runtime ReferenceError with no build signal).

Specs load lib/*.js by evaluating the real file as a classic script
(test/helpers/loadLib.js) instead of adding module.exports shims to production
code that would never run in the browser. The suite therefore exercises exactly
the bytes packaged into the XPI.

Two packaging consequences, both handled:

- web-ext would otherwise bundle test/ and vitest.config.js INTO the XPI;
  both are now in --ignore-files across all four web-ext scripts.
- ci.yml's extension-version guard must ignore the same paths, or editing a
  spec would demand a pointless version bump. The dangerous drift direction is
  the opposite one -- a guard exclusion for a file that DOES ship would let a
  real change pass unnoticed -- so version.spec.js asserts every :(exclude) in
  ci.yml appears in --ignore-files.

extension.yml also triggers on ci.yml now, since version.spec.js reads it.

Refs #2393, #2397

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

.forgejo/workflows/ci.yml

@@ -123,13 +123,18 @@ jobs:
           fi
           # Exclusions mirror --ignore-files in extension/package.json's web-ext
           # scripts: these files are not packaged into the XPI, so touching them
-          # (e.g. Renovate bumping the web-ext devDep) changes nothing shipped
-          # and must not demand a version bump.
+          # (e.g. Renovate bumping the web-ext devDep, or editing a spec)
+          # changes nothing shipped and must not demand a version bump.
+          # KEEP IN SYNC with --ignore-files — a file packaged into the XPI but
+          # excluded here is exactly the silent-stale-ship this job exists to
+          # prevent. test/version.spec.js pins the two lists' shared intent.
           CHANGED=$(git diff --name-only "$BASE" HEAD -- extension/ \
             ':(exclude)extension/package.json' \
             ':(exclude)extension/package-lock.json' \
             ':(exclude)extension/README.md' \
-            ':(exclude)extension/.gitignore')
+            ':(exclude)extension/.gitignore' \
+            ':(exclude)extension/vitest.config.js' \
+            ':(exclude)extension/test/**')
           if [ -z "$CHANGED" ]; then
             echo "No packaged extension files changed since $BASE — nothing to guard."
             echo "OK: extension version $PKG"

.forgejo/workflows/extension.yml

@@ -1,5 +1,5 @@
 name: extension
-# Lint-only workflow. The sign-and-publish dance moved into build.yml's
+# Lint + unit tests. The sign-and-publish dance moved into build.yml's
 # `sign-extension` job (2026-05-25) — `:latest` now always bundles the XPI
 # because sign-extension runs as a build-web dependency in the SAME workflow,
 # eliminating the prior race between build.yml and a separate extension.yml.
@@ -10,10 +10,15 @@ on:
     paths:
       - 'extension/**'
       - '.forgejo/workflows/extension.yml'
+      # test/version.spec.js asserts ci.yml's extension-version guard never
+      # ignores a file web-ext actually packages, so a ci.yml-only edit can
+      # break this suite and must trigger it.
+      - '.forgejo/workflows/ci.yml'
   pull_request:
     branches: [main]
     paths:
       - 'extension/**'
+      - '.forgejo/workflows/ci.yml'
   workflow_dispatch:
 
 jobs:
@@ -23,7 +28,13 @@ jobs:
       image: node:24-bookworm-slim
     steps:
       - uses: actions/checkout@v4
-      - name: Install web-ext
-        run: cd extension && npm install --no-save --no-audit --no-fund
+      # Not --no-save: vitest and web-ext are both real devDependencies now,
+      # and the suite needs vitest resolvable from node_modules.
+      - name: Install dev dependencies
+        run: cd extension && npm install --no-audit --no-fund
       - name: Lint
         run: cd extension && npm run lint
+      # Pure-logic specs over lib/url.js and lib/platforms.js plus manifest /
+      # package version-consistency checks. No browser, no network.
+      - name: Unit tests
+        run: cd extension && npm run test:unit