Add feature batch 2, subscription/recurring sync, smooth charts, and app icon

- Implement subscriptions view with bidirectional recurring transaction sync
- Add cascade delete/pause/resume between subscriptions and recurring
- Fix foreign key constraints when deleting recurring transactions
- Add cross-view instant refresh via callback pattern
- Replace Bezier chart smoothing with Fritsch-Carlson monotone Hermite interpolation
- Smooth budget sparklines using shared monotone_subdivide function
- Add vertical spacing to budget rows
- Add app icon (receipt on GNOME blue) in all sizes for desktop, web, and AppImage
- Add calendar, credit cards, forecast, goals, insights, and wishlist views
- Add date picker, numpad, quick-add, category combo, and edit dialog components
- Add import/export for CSV, JSON, OFX, QIF formats
- Add NLP transaction parsing, OCR receipt scanning, expression evaluator
- Add notification support, Sankey chart, tray icon
- Add demo data seeder with full DB wipe
- Expand database schema with subscriptions, goals, credit cards, and more

outlay-core/src/import_json.rs

@@ -0,0 +1,59 @@
+use crate::db::Database;
+use crate::export_json::ExportData;
+use crate::models::{NewCategory, NewTransaction};
+use std::path::Path;
+
+pub fn import_json(db: &Database, path: &Path, merge: bool) -> Result<usize, Box<dyn std::error::Error>> {
+    let content = std::fs::read_to_string(path)?;
+    let data: ExportData = serde_json::from_str(&content)?;
+
+    if !merge {
+        db.reset_all_data()?;
+    }
+
+    for cat in &data.categories {
+        let existing = db.list_categories(Some(cat.transaction_type))?;
+        if !existing.iter().any(|c| c.name == cat.name) {
+            let new_cat = NewCategory {
+                name: cat.name.clone(),
+                icon: cat.icon.clone(),
+                color: cat.color.clone(),
+                transaction_type: cat.transaction_type,
+                sort_order: cat.sort_order,
+                parent_id: None,
+            };
+            db.insert_category(&new_cat)?;
+        }
+    }
+
+    let mut count = 0;
+    for txn in &data.transactions {
+        let categories = db.list_categories(Some(txn.transaction_type))?;
+        let original_cat = data.categories.iter().find(|c| c.id == txn.category_id);
+        let category_id = match original_cat {
+            Some(oc) => categories.iter().find(|c| c.name == oc.name).map(|c| c.id),
+            None => None,
+        };
+        let Some(category_id) = category_id else { continue };
+
+        if merge && db.find_duplicate_transaction(txn.amount, txn.transaction_type, category_id, txn.date)? {
+            continue;
+        }
+
+        let new_txn = NewTransaction {
+            amount: txn.amount,
+            transaction_type: txn.transaction_type,
+            category_id,
+            currency: txn.currency.clone(),
+            exchange_rate: txn.exchange_rate,
+            note: txn.note.clone(),
+            date: txn.date,
+            recurring_id: None,
+            payee: txn.payee.clone(),
+        };
+        db.insert_transaction(&new_txn)?;
+        count += 1;
+    }
+
+    Ok(count)
+}