fix(extension): normalize FC URL so credential push doesn't 405

The stored apiUrl was required to already carry the `/api` suffix, since
api.js builds requests as `${baseUrl}/credentials`. The options label read
"FC base URL", so entering the instance root -- the natural reading --
sent every request one path segment short: POST /credentials hit the Vue
SPA catch-all and came back 405, and GET /extension/manifest 404'd.

Worse, Test Connection reported success on it: the catch-all answers GET
/credentials with 200 HTML, so `r.ok` was true and the only affordance
meant to catch this misconfiguration actively masked it.

Normalize instead of validate (rules 92, 26):

- New lib/url.js: normalizeApiUrl / webRootFromApiUrl, one source shared
  by the background client and the options page. Accepts either the
  instance root or the API root.
- api.js normalizes on read, so configs already stored in the broken form
  heal themselves without the operator reopening Settings.
- options.js stores the canonical form, echoes back what it saved, and
  the test now asserts a JSON content-type -- killing the false green.
- 404/405 in request() now names the URL and points at the setting.
- Options label/placeholder state that both forms work.

Version 1.0.9 -> 1.0.10 in BOTH manifest.json and package.json; build.yml
resolves the release version from package.json, and a stale value there
would hit the cached ext-1.0.9 asset and republish the old XPI unsigned
against the new code.

Refs #2393

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

extension/options/options.js

@@ -8,7 +8,7 @@ document.addEventListener('DOMContentLoaded', async () => {
 });
 
 async function save() {
-  const apiUrl = document.getElementById('api-url').value.trim().replace(/\/+$/, '');
+  const apiUrl = normalizeApiUrl(document.getElementById('api-url').value);
   const apiKey = document.getElementById('api-key').value.trim();
   if (!apiUrl || !apiKey) {
     showStatus('Both fields are required.', 'err');
@@ -16,11 +16,14 @@ async function save() {
   }
   await browser.storage.local.set({ apiUrl, apiKey });
   await browser.storage.local.remove(['lastConnectionTest', 'lastConnectionStatus']);
-  showStatus('Saved.', 'ok');
+  // Show what was actually stored — the operator may have typed the instance
+  // root and it was normalized to the API root.
+  document.getElementById('api-url').value = apiUrl;
+  showStatus(`Saved — using ${apiUrl}`, 'ok');
 }
 
 async function test() {
-  const apiUrl = document.getElementById('api-url').value.trim().replace(/\/+$/, '');
+  const apiUrl = normalizeApiUrl(document.getElementById('api-url').value);
   const apiKey = document.getElementById('api-key').value.trim();
   if (!apiUrl || !apiKey) {
     showStatus('Fill both fields first.', 'err');
@@ -31,8 +34,23 @@ async function test() {
       method: 'GET',
       headers: { 'X-Extension-Key': apiKey },
     });
-    if (r.ok) showStatus(`Connected — HTTP ${r.status}.`, 'ok');
-    else showStatus(`HTTP ${r.status}: ${r.statusText}`, 'err');
+    if (!r.ok) {
+      showStatus(`HTTP ${r.status}: ${r.statusText}`, 'err');
+      return;
+    }
+    // A 200 is NOT sufficient. If the URL resolves to the Vue SPA instead of
+    // the JSON API, the catch-all route returns 200 with an HTML document —
+    // which used to report "Connected" on a config that could not POST at all.
+    const contentType = r.headers.get('content-type') || '';
+    if (!contentType.includes('json')) {
+      showStatus(
+        `${apiUrl} answered with ${contentType || 'no content-type'}, not JSON `
+          + '— that looks like the FC web UI rather than its API.',
+        'err',
+      );
+      return;
+    }
+    showStatus(`Connected to ${apiUrl} — HTTP ${r.status}.`, 'ok');
   } catch (e) {
     showStatus(`Cannot reach ${apiUrl}: ${e.message}`, 'err');
   }