Expand Sale/Purchase/Project + 102 ORM tests — +4633 LOC

Sale (1177→2321 LOC):
- Quotation templates (apply to order, option lines)
- Sales reports (by month, product, customer, salesperson, category)
- Advance payment wizard (delivered/percentage/fixed modes)
- SO cancel wizard, discount wizard
- action_quotation_sent, action_lock/unlock, preview_quotation
- Line computes: invoice_status, price_reduce, untaxed_amount
- Partner extension: sale_order_total

Purchase (478→1424 LOC):
- Purchase reports (by month, category, bill status, receipt analysis)
- Receipt creation from PO (action_create_picking)
- 3-way matching: action_view_picking, action_view_invoice
- button_approve, button_done, action_rfq_send
- Line computes: price_subtotal/total with tax, product onchange
- Partner extension: purchase_order_count/total

Project (218→1161 LOC):
- Project updates (status tracking: on_track/at_risk/off_track)
- Milestones (deadline, reached tracking, task count)
- Timesheet integration (account.analytic.line extension)
- Timesheet reports (by project, employee, task, week)
- Task recurrence model
- Task: planned/effective/remaining hours, progress, subtask hours
- Project: allocated/remaining hours, profitability actions

ORM Tests (102 tests, 0→1257 LOC):
- domain_test.go: 32 tests (compile, operators, AND/OR/NOT, null)
- field_test.go: 15 tests (IsCopyable, SQLType, IsRelational, IsStored)
- model_test.go: 21 tests (NewModel, AddFields, RegisterMethod, ExtendModel)
- domain_parse_test.go: 21 tests (parse Python domain strings)
- sanitize_test.go: 13 tests (false→nil, type conversions)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

addons/purchase/models/init.go

@@ -4,4 +4,9 @@ func Init() {
 	initPurchaseOrder()
 	initPurchaseOrderLine()
 	initPurchaseAgreement()
+	initPurchaseReport()
+	initPurchaseOrderExtension()
+	initPurchaseOrderLineExtension()
+	initResPartnerPurchaseExtension()
+	initPurchaseOrderAmount()
 }