test(client): check what the chunk registers, and fix two defects in the checks

Three things, all about checks that had never met a real chunk.

`checkExternals.js` rejected slice 3's build outright, naming a fragment of
minified JSX as an imported specifier: a button reading "Approve and import"
puts the token immediately before a quote, and no regexp can tell that from a
statement. Same wall the server's `checkImports.js` hit, answered the same way —
a character walk. A mask rather than a rewrite, because a real import has its
keyword outside a string and its specifier inside one.

Writing the test for that false positive found the false NEGATIVE underneath
it: the pattern required whitespace after `import`, so it could not see
`import{useState}from"react"` — the one shape a minified build actually emits,
and the most likely way for a missed alias to reach production. It has never
been able to see it.

`registration.test.js` is new: stand up a fake `window.__rg` with a recording
registry and the real React, import the BUILT chunk, and read back what it
asked for. No DOM, because nothing renders. It holds the agreement that rots
quietly — every nav row points at a route this module actually registered —
rather than restating both lists.

CI now builds before it tests, because both of those read `dist/entry.js` and
skip without it. Run the other way round they are green and asking nothing.

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

.gitea/workflows/pr-checks.yml

@@ -94,11 +94,16 @@ jobs:
       - name: Install client deps
         run: npm ci --prefix client
 
-      - name: Run client tests
-        run: npm test --prefix client
-
+      # The build comes FIRST, and that ordering is load-bearing as of slice 3.
+      # Two of the client tests read `dist/entry.js` — the chunk's externals, and
+      # what it registers when imported against a fake `window.__rg` — and both
+      # skip when there is no build. Run the other way round they skip silently
+      # in CI, which is the worst of both: green, and not asking the question.
       - name: Build the client chunk
         run: npm run build --prefix client
 
+      - name: Run client tests
+        run: npm test --prefix client
+
       - name: Check the built chunk's externals (MODULE_API.md §3.6)
         run: npm run check:externals --prefix client