Add browser extension and shell completions (Milestones 12-13)

M12: Browser Extension
- Chrome/Edge Manifest V3 extension
- Popup UI for saving pages
- Context menu integration (save page/selection/link)
- Background service worker
- Content script for extraction

M13: Shell Completions
- Bash, Zsh, Fish, PowerShell completions
- Dynamic node ID completion
- Dynamic tag completion
- Dynamic graph completion
- Auto-install command (--install)

extension/popup/popup.js

@@ -0,0 +1,136 @@
+// Popup script for Cortex browser extension
+
+const CORTEX_API = 'http://localhost:3100/api';
+
+// DOM elements
+const titleInput = document.getElementById('title');
+const kindSelect = document.getElementById('kind');
+const tagsInput = document.getElementById('tags');
+const includeContent = document.getElementById('includeContent');
+const selectionOnly = document.getElementById('selectionOnly');
+const saveButton = document.getElementById('save');
+const cancelButton = document.getElementById('cancel');
+const statusDiv = document.getElementById('status');
+
+let pageData = null;
+
+// Initialize popup
+async function init() {
+  try {
+    // Get current tab
+    const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+
+    // Request content from content script
+    const response = await chrome.tabs.sendMessage(tab.id, { action: 'extract' });
+    pageData = response;
+
+    // Pre-fill form
+    titleInput.value = response.title || tab.title || '';
+
+    // Suggest tags based on URL
+    const url = new URL(tab.url);
+    const suggestedTags = ['web-clip'];
+    if (url.hostname.includes('github')) suggestedTags.push('github');
+    if (url.hostname.includes('docs')) suggestedTags.push('documentation');
+    if (url.hostname.includes('stackoverflow')) suggestedTags.push('stackoverflow');
+    tagsInput.value = suggestedTags.join(', ');
+
+    // Enable selection only if there's selected text
+    if (response.selection) {
+      selectionOnly.disabled = false;
+    } else {
+      selectionOnly.disabled = true;
+    }
+
+  } catch (err) {
+    showStatus('Could not extract page content', 'error');
+    console.error('Init error:', err);
+  }
+}
+
+// Save to Cortex
+async function save() {
+  saveButton.disabled = true;
+  saveButton.textContent = 'Saving...';
+
+  try {
+    const content = selectionOnly.checked
+      ? pageData?.selection
+      : (includeContent.checked ? pageData?.content : '');
+
+    const tags = tagsInput.value
+      .split(',')
+      .map(t => t.trim())
+      .filter(t => t.length > 0);
+
+    const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+
+    const response = await fetch(`${CORTEX_API}/nodes`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+      },
+      body: JSON.stringify({
+        kind: kindSelect.value,
+        title: titleInput.value,
+        content: content,
+        tags: tags,
+        metadata: {
+          source: {
+            type: 'url',
+            url: tab.url,
+            savedAt: Date.now(),
+          },
+        },
+      }),
+    });
+
+    if (!response.ok) {
+      throw new Error(`HTTP ${response.status}`);
+    }
+
+    const node = await response.json();
+    showStatus(`Saved! ID: ${node.id.slice(0, 8)}`, 'success');
+
+    // Close popup after brief delay
+    setTimeout(() => window.close(), 1500);
+
+  } catch (err) {
+    showStatus(`Failed to save: ${err.message}`, 'error');
+    console.error('Save error:', err);
+
+    // Check if Cortex server is running
+    if (err.message.includes('fetch')) {
+      showStatus('Is Cortex server running? (cortex serve)', 'error');
+    }
+  } finally {
+    saveButton.disabled = false;
+    saveButton.textContent = 'Save';
+  }
+}
+
+// Show status message
+function showStatus(message, type) {
+  statusDiv.textContent = message;
+  statusDiv.className = `status ${type}`;
+}
+
+// Event listeners
+saveButton.addEventListener('click', save);
+cancelButton.addEventListener('click', () => window.close());
+
+// Toggle selection only checkbox when include content is unchecked
+includeContent.addEventListener('change', () => {
+  if (!includeContent.checked) {
+    selectionOnly.checked = false;
+  }
+});
+
+selectionOnly.addEventListener('change', () => {
+  if (selectionOnly.checked) {
+    includeContent.checked = true;
+  }
+});
+
+// Initialize on load
+init();