feat: add Playwright agent testability infrastructure

Add test harness (window.__bitvidTest__), data-testid attributes, relay
override support, and Playwright fixtures so agents can programmatically
login, seed relay data, and inspect app state during E2E testing.

- js/testHarness.js: exposes loginWithNsec, getAppState, relay overrides
- data-testid attrs on login/upload/video modals, header buttons, feed
- simple-relay.mjs: HTTP seeding API (POST /seed, GET /events, /health)
- bitvidTestFixture.ts: reusable Playwright fixture with mock relay
- agent-testability.spec.ts: E2E tests validating the infrastructure

https://claude.ai/code/session_01XnrszNmdqrAGd8g8qhAn4G

components/login-modal.html

@@ -6,6 +6,7 @@
   aria-labelledby="loginModalTitle"
   aria-describedby="loginModalDescription"
   data-ds="new"
+  data-testid="login-modal"
 >
   <div class="bv-modal-backdrop" data-dismiss></div>
 
@@ -91,6 +92,7 @@
           class="login-option"
           type="button"
           data-provider-button
+          data-testid="login-provider-button"
         >
           <span class="login-option__header">
             <span class="login-option__copy">
@@ -204,6 +206,7 @@
                 spellcheck="false"
                 autocomplete="off"
                 data-nsec-secret
+                data-testid="nsec-secret-input"
               ></textarea>
               <label class="inline-flex items-center gap-2 text-sm text-text">
                 <input type="checkbox" class="checkbox" data-nsec-remember />
@@ -235,7 +238,7 @@
           </fieldset>
           <div class="flex justify-end gap-2">
             <button type="button" class="btn-ghost" data-nsec-cancel>Cancel</button>
-            <button type="submit" class="btn" data-nsec-submit>Continue</button>
+            <button type="submit" class="btn" data-nsec-submit data-testid="nsec-submit">Continue</button>
           </div>
         </form>
       </template>

components/upload-modal.html

@@ -7,6 +7,7 @@
   aria-labelledby="uploadModalTitle"
   aria-describedby="uploadModalDescription"
   data-ds="new"
+  data-testid="upload-modal"
 >
   <div class="bv-modal-backdrop" data-dismiss></div>
 
@@ -192,12 +193,12 @@
             <div id="section-source-external" class="space-y-4 hidden">
                  <div class="space-y-2">
                     <label for="input-url" class="block text-sm font-medium text-text">Video URL</label>
-                    <input id="input-url" type="url" class="input" placeholder="https://example.com/video.mp4" />
+                    <input id="input-url" type="url" class="input" placeholder="https://example.com/video.mp4" data-testid="upload-url" />
                     <p class="text-xs text-muted">Primary hosted video source (URL-first playback).</p>
                 </div>
                  <div class="space-y-2">
                     <label for="input-magnet" class="block text-sm font-medium text-text">Magnet Link</label>
-                    <input id="input-magnet" type="text" class="input" placeholder="magnet:?xt=urn:btih:..." />
+                    <input id="input-magnet" type="text" class="input" placeholder="magnet:?xt=urn:btih:..." data-testid="upload-magnet" />
                     <p class="text-xs text-muted">Optional WebTorrent fallback when the URL is unavailable.</p>
                 </div>
             </div>
@@ -208,7 +209,7 @@
             <div class="space-y-4">
                 <div class="space-y-2">
                     <label for="input-title" class="block text-sm font-medium text-text">Title</label>
-                    <input id="input-title" type="text" required class="input" placeholder="Give your video a title" />
+                    <input id="input-title" type="text" required class="input" placeholder="Give your video a title" data-testid="upload-title" />
                 </div>
 
                 <div class="space-y-2">
@@ -388,7 +389,7 @@
 
             <!-- Submit -->
             <div class="pt-4">
-                <button type="submit" id="btn-submit" class="btn w-full py-3 text-base font-semibold shadow-md">
+                <button type="submit" id="btn-submit" class="btn w-full py-3 text-base font-semibold shadow-md" data-testid="upload-submit">
                     Publish Video
                 </button>
                 <p id="submit-status" class="text-center text-xs text-muted mt-2"></p>

components/video-modal.html

@@ -5,6 +5,7 @@
   role="dialog"
   aria-modal="true"
   data-ds="new"
+  data-testid="video-modal"
   hidden
 >
   <div class="bv-modal-backdrop" data-dismiss></div>