feat: Make galaxy viewable without login requirement

Implemented public galaxy viewing feature that allows unauthenticated
users to view public thought galaxies via the ?user={did} parameter,
while maintaining privacy controls for node-level visibility.

Changes:
- Updated /api/galaxy/route.ts to support public access:
  * Accept ?user={did} query parameter for viewing specific user's galaxy
  * Show all nodes (including private) for authenticated user viewing own galaxy
  * Filter to only public nodes when viewing someone else's galaxy
  * Return empty state with helpful message when not authenticated
  * Filter links to only show connections between visible nodes

- Added is_public field to database schema:
  * Updated db/schema.surql with DEFAULT true (public by default)
  * Created migration script scripts/add-is-public-field.ts
  * Aligns with ATproto's public-by-default philosophy

- Enhanced ThoughtGalaxy component:
  * Support viewing galaxies via ?user={did} parameter
  * Display user info banner when viewing public galaxy
  * Show appropriate empty state messages based on context
  * Refetch data when user parameter changes

- Created comprehensive Magnitude tests:
  * Test public galaxy viewing without authentication
  * Verify private nodes are hidden from public view
  * Test own galaxy access requires authentication
  * Validate invalid user DID handling
  * Test user info display and navigation between galaxies

- Documented implementation plan in plans/10-public-galaxy-viewing.md

This implements the "public by default" model while allowing future
node-level privacy controls. All canonical data remains on the user's
ATproto PDS, with SurrealDB serving as a high-performance cache.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/ThoughtGalaxy.tsx

@@ -95,18 +95,25 @@ export function ThoughtGalaxy() {
   const [nodes, setNodes] = useState<NodeData[]>([]);
   const [links, setLinks] = useState<LinkData[]>([]);
   const [selectedNode, setSelectedNode] = useState<NodeData | null>(null);
+  const [emptyMessage, setEmptyMessage] = useState<string | null>(null);
   const cameraControlsRef = useRef<CameraControls>(null);
   const hasFitCamera = useRef(false);
   const hasFocusedNode = useRef<string | null>(null);
 
-  // Get selectedNodeId from URL query params
+  // Get query params
   const selectedNodeId = searchParams.get('node');
+  const targetUserDid = searchParams.get('user'); // For viewing someone else's galaxy
 
   // Fetch data from API on mount and poll for updates
   useEffect(() => {
     async function fetchData() {
       try {
-        const response = await fetch('/api/galaxy', {
+        // Build URL with optional user parameter
+        const url = targetUserDid
+          ? `/api/galaxy?user=${encodeURIComponent(targetUserDid)}`
+          : '/api/galaxy';
+
+        const response = await fetch(url, {
           credentials: 'include', // Include cookies for authentication
         });
 
@@ -119,13 +126,17 @@ export function ThoughtGalaxy() {
 
         if (data.message) {
           console.log('[ThoughtGalaxy]', data.message);
+          setEmptyMessage(data.message);
           // If calculating, poll again in 2 seconds
-          setTimeout(fetchData, 2000);
+          if (data.message.includes('calculating')) {
+            setTimeout(fetchData, 2000);
+          }
           return;
         }
 
         setNodes(data.nodes || []);
         setLinks(data.links || []);
+        setEmptyMessage(null);
 
         console.log(`[ThoughtGalaxy] Loaded ${data.nodes?.length || 0} nodes and ${data.links?.length || 0} links`);
       } catch (error) {
@@ -134,7 +145,7 @@ export function ThoughtGalaxy() {
     }
 
     fetchData();
-  }, []);
+  }, [targetUserDid]);
 
   // Function to fit camera to all nodes
   const fitCameraToNodes = () => {
@@ -286,17 +297,49 @@ export function ThoughtGalaxy() {
     return (
       <Stack align="center" justify="center" style={{ height: '100vh', width: '100vw' }}>
         <MantineText size="lg" c="dimmed">
-          Create at least 3 nodes to visualize your thought galaxy
-        </MantineText>
-        <MantineText size="sm" c="dimmed">
-          Nodes with content will automatically generate embeddings and 3D coordinates
+          {emptyMessage || 'Create at least 3 nodes to visualize your thought galaxy'}
         </MantineText>
+        {!emptyMessage && (
+          <MantineText size="sm" c="dimmed">
+            Nodes with content will automatically generate embeddings and 3D coordinates
+          </MantineText>
+        )}
+        {targetUserDid && (
+          <MantineText size="sm" c="dimmed" mt="xs">
+            Viewing galaxy for user: {targetUserDid}
+          </MantineText>
+        )}
       </Stack>
     );
   }
 
   return (
     <>
+      {/* User info banner when viewing someone else's galaxy */}
+      {targetUserDid && (
+        <Box
+          style={{
+            position: 'absolute',
+            top: '10px',
+            right: '10px',
+            zIndex: 999,
+            maxWidth: '300px',
+          }}
+        >
+          <Paper p="sm" radius="md" withBorder shadow="md">
+            <MantineText size="sm" fw={600}>
+              Public Galaxy
+            </MantineText>
+            <MantineText size="xs" c="dimmed">
+              Viewing {nodes.length} public {nodes.length === 1 ? 'node' : 'nodes'}
+            </MantineText>
+            <MantineText size="xs" c="dimmed" style={{ wordBreak: 'break-all' }}>
+              {targetUserDid}
+            </MantineText>
+          </Paper>
+        </Box>
+      )}
+
       {/* Floating content overlay for selected node */}
       {selectedNode && (
         <Box