fix: budget save error and add read-only view mode (v2026.03.10)

Fix budget save 500 error caused by three data mismatches between
frontend and backend: wrapped payload ({lines:[...]}) vs expected
raw array, snake_case vs camelCase field names (account_id vs
accountId), and dec_amt vs dec for December values.

Add read-only budget view as default for existing budgets with an
"Edit Budget" button to enter edit mode, and Cancel to discard
changes - reducing accidental edits.

Bump version to 2026.03.10 across all packages and settings.

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

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "hoa-ledgeriq-backend",
-  "version": "2026.3.7-beta",
+  "version": "2026.03.10",
   "description": "HOA LedgerIQ - Backend API",
   "private": true,
   "scripts": {