Improve metadata prompts; fix upload error + remove debug log

- Replace bracketed metadata placeholders with prompting questions
- Fix upload error message (response.statusContents -> statusText)
- Remove stray debug console.log on reactive screen updates
- Document the upload token's security model in the app README

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bicorder-app/src/App.svelte

@@ -77,11 +77,6 @@
   $: currentScreenData = screens[currentScreen];
   $: totalScreens = screens.length;
 
-  // Debug: log when screens change
-  $: if (screens) {
-    console.log(`Screens updated: ${screens.length} total, shortform: ${data.metadata.shortform}`);
-  }
-
   function goToNextScreen() {
     if (currentScreen < totalScreens - 1) {
       currentScreen++;

bicorder-app/src/components/ExportControls.svelte

@@ -83,7 +83,7 @@
         showUploadDialog = false;
       } else {
         const errorData = await response.json();
-        throw new Error(errorData.message || `Upload failed: ${response.statusContents}`);
+        throw new Error(errorData.message || `Upload failed: ${response.statusText}`);
       }
     } catch (err) {
       console.error('Upload error:', err);

bicorder-app/src/components/MetadataFields.svelte

@@ -36,7 +36,7 @@
     <input
       id="protocol"
       type="text"
-      placeholder="[Protocol]"
+      placeholder="What protocol are you analyzing?"
       value={metadata.protocol || ''}
       on:input={(e) => handleInput('protocol', e.currentTarget.value)}
     />
@@ -46,7 +46,7 @@
     <label for="description">Description:</label>
     <textarea
       id="description"
-      placeholder="[Description]"
+      placeholder="Briefly, what is this protocol?"
       value={metadata.description || ''}
       on:input={(e) => handleInput('description', e.currentTarget.value)}
       rows="3"
@@ -58,7 +58,7 @@
     <input
       id="analyst"
       type="text"
-      placeholder="[Analyst]"
+      placeholder="How do you identify yourself?"
       value={metadata.analyst || ''}
       on:input={(e) => handleInput('analyst', e.currentTarget.value)}
     />
@@ -69,7 +69,7 @@
     <input
       id="standpoint"
       type="text"
-      placeholder="[Standpoint]"
+      placeholder="What is your relationship to the protocol?"
       value={metadata.standpoint || ''}
       on:input={(e) => handleInput('standpoint', e.currentTarget.value)}
     />