Add issue/cancel lifecycle, GST derivation and integer-paise totals

issue_invoice allocates the number, freezes vendor and bank details and
stores server-computed totals in one transaction. Issued invoices are
cancelled, not deleted. Tax heads derive from supplier state and place of
supply (a disagreeing choice is rejected); unregistered suppliers issue a
plain Invoice. Adds GSTIN checksum validation, canonical India Compliance
state list, server-side drafts, series validation, relative and
magic-byte-checked asset paths, and GST settings. PDF re-exports use the
frozen vendor snapshot.

src-tauri/src/models.rs

@@ -96,6 +96,8 @@ pub struct InvoiceItem {
     pub amount: f64,
     #[serde(default)]
     pub sort_order: i64,
+    #[serde(default)]
+    pub hsn_sac: String,
 }
 
 fn default_mode() -> String {
@@ -106,6 +108,8 @@ fn default_unit() -> String {
     "unit".to_string()
 }
 
+/// What the webview may send when issuing an invoice. Money totals, tax amounts,
+/// the amount in words and the vendor/bank snapshots are derived on the Rust side.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct InvoiceInput {
@@ -125,34 +129,25 @@ pub struct InvoiceInput {
     #[serde(default)]
     pub place_of_supply_state_code: String,
     #[serde(default)]
-    pub subtotal: f64,
-    #[serde(default)]
     pub discount: f64,
+    /// The tax treatment the user chose; it must match the derived one.
     #[serde(default = "default_tax_type")]
     pub tax_type: String,
     #[serde(default)]
     pub tax_rate: f64,
     #[serde(default)]
-    pub cgst_amount: f64,
-    #[serde(default)]
-    pub sgst_amount: f64,
-    #[serde(default)]
-    pub igst_amount: f64,
-    #[serde(default)]
-    pub total: f64,
-    #[serde(default)]
-    pub amount_in_words: String,
+    pub reverse_charge: bool,
     #[serde(default)]
     pub bank_account_id: Option<i64>,
     #[serde(default)]
-    pub bank_snapshot: String,
-    #[serde(default)]
     pub signature_path: Option<String>,
     #[serde(default)]
     pub notes: String,
     #[serde(default)]
     pub save_client: bool,
     #[serde(default)]
+    pub draft_id: Option<i64>,
+    #[serde(default)]
     pub items: Vec<InvoiceItem>,
 }
 
@@ -187,9 +182,18 @@ pub struct Invoice {
     pub bank_snapshot: String,
     pub signature_path: Option<String>,
     pub notes: String,
+    /// draft | issued | cancelled
     pub status: String,
     pub created_at: String,
     pub updated_at: String,
+    pub doc_type: String,
+    pub reverse_charge: bool,
+    /// JSON of the supplier details as they were when the invoice was issued; empty if unknown.
+    pub vendor_snapshot: String,
+    pub snapshot_origin: String,
+    pub cancelled_at: Option<String>,
+    pub cancel_reason: String,
+    pub archived_pdf_sha256: Option<String>,
     pub items: Vec<InvoiceItem>,
 }
 
@@ -205,3 +209,12 @@ pub struct InvoiceSummary {
     pub status: String,
     pub created_at: String,
 }
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct DraftSummary {
+    pub id: i64,
+    pub updated_at: String,
+    pub client_name: Option<String>,
+    pub total: Option<f64>,
+}