feat: plot sales lifecycle v2 close/terminate, payment sync, cost tracking, TCB v0.6

[github-actions]

Backport of #38 to version-15.

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Summary

This PR completes the core plot sales lifecycle and fixes several accounting
issues discovered during testing.

Sales Order Close & Contract Termination

• Added Close Sales Order button (Actions menu) with full downstream effects:
  forfeiture JE, credit note, TCB decline, plot release, PA cancellation
• Fixed contract termination to set SO status = Closed (not Cancel) so all
  accounting entries are preserved as audit trail
• Credit note now correctly zeros SI outstanding via update_outstanding_for_self=0
• Fixed draft contract total_paid persistence — _persist_payment_sync_state
  now uses db.set_value instead of save() to prevent validate() resetting values
• Removed incorrect advance row zeroing from _sync_contract_after_payment

Payment Sync

• Moved from background job to synchronous execution — eliminates
  TimestampMismatchError from concurrent syncs and worker dependency
• Overpayment now detected via pe.unallocated_amount and shown on Plot Contract
• SI payment schedule rows synced alongside SO rows on each payment
• cost_center auto-enforced on all JE rows where land_acquisition is set

Government Share JE

• Auto-posted per payment at government_share_percent
• Cancelled automatically when the linked Payment Entry is cancelled

TCB v0.6

• paymentOption (Partial/Exact), expireDate, amount wired to Sales Order fields
• All three fields are optional — only sent to TCB when explicitly set

Land Acquisition Cost Tracking

• JE amounts now included in acquisition_cost_tzs via _fetch_billed_from_je
• je_billed_tzs field added to LA form with drill-down table showing each JE
• Recalculate Plot Costs button: background job that updates stock valuations
  for unsold plots when late PIs arrive; skips delivered/Title Closed plots
• cost_per_sqm now updated on all plots including unchanged-cost ones

Reports & UI

• Government Payable report rebuilt for per-payment JE model with LA filter
• Title Closed folded into Delivered in all counts and reports
• Sales Invoice before_save hook: clears deferred revenue fields, restores
  Balance payment schedule row if ERPNext collapsed it
• Journal Entry before_save hook: enforces LandMS cost center on LA rows