Add project soft-delete with workspace archival

- Add delete button (×) to sidebar project list, shown on hover
- Soft-delete: mark projects as deleted in DB instead of hard delete
- Move workspace files to /app/data/deleted/ folder on deletion
- Filter deleted projects from list query
- Auto-select next project after deleting current one
- Also includes agent prompt improvements for reverse proxy paths

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

src/db.rs

@@ -94,6 +94,13 @@ impl Database {
         .execute(&self.pool)
         .await;
 
+        // Migration: add deleted column to projects
+        let _ = sqlx::query(
+            "ALTER TABLE projects ADD COLUMN deleted INTEGER NOT NULL DEFAULT 0"
+        )
+        .execute(&self.pool)
+        .await;
+
         sqlx::query(
             "CREATE TABLE IF NOT EXISTS timers (
                 id TEXT PRIMARY KEY,
@@ -120,6 +127,8 @@ pub struct Project {
     pub description: String,
     pub created_at: String,
     pub updated_at: String,
+    #[serde(default)]
+    pub deleted: bool,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]