Add side panels, task selection, graph animation, and project docs

- Foldable left panel (user profile) and right panel (task details)
- Clicking a task in the list or graph node selects it and shows details
- Both views (task list + graph) always mounted via absolute inset-0 for
  correct canvas dimensions; tabs toggle visibility with opacity
- Graph node selection animation: other nodes repel outward (charge -600),
  then selected node smoothly slides to center (500ms cubic ease-out),
  then charge restores to -120 and graph stabilizes
- Graph re-fits on tab switch and panel resize via ResizeObserver
- Fix UUID string IDs throughout (backend returns UUIDs, not integers)
- Add TaskDetailPanel, UserPanel components
- Add CLAUDE.md project documentation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/db.rs

@@ -0,0 +1,27 @@
+use anyhow::Result;
+use sqlx::{sqlite::SqlitePoolOptions, SqlitePool};
+
+pub async fn create_pool(database_url: &str) -> Result<SqlitePool> {
+    let pool = SqlitePoolOptions::new()
+        .max_connections(5)
+        .connect(database_url)
+        .await?;
+    Ok(pool)
+}
+
+pub async fn run_migrations(pool: &SqlitePool) -> Result<()> {
+    sqlx::query(
+        r#"
+        CREATE TABLE IF NOT EXISTS tasks (
+            id          TEXT PRIMARY KEY NOT NULL,
+            title       TEXT NOT NULL,
+            description TEXT,
+            completed   BOOLEAN NOT NULL DEFAULT 0,
+            created_at  INTEGER NOT NULL
+        )
+        "#,
+    )
+    .execute(pool)
+    .await?;
+    Ok(())
+}