fix: use System Settings currency as CRM base currency instead of defaulting to USD

[Shindhu-Ramaswamy]

Fixes #1117

Changes

• Add get_base_currency() in crm/utils — resolves FCRM Settings.currency → System Settings.currency → USD, and use it in the dashboard, Deal and Organization exchange-rate code instead of the hard-coded USD fallback.
• Seed FCRM Settings.currency from System Settings on after_install and on setup_wizard_complete (the wizard runs after install on a fresh site).
• Patch to backfill the currency for existing sites that never set one.
• Tests for the fallback order and the seeding logic.

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

_{Reviews (1) · Last reviewed commit: "fix: use System Settings currency as CRM..."}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.18182% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.29%. Comparing base (4ddcbbc) to head (46354a7).

Files with missing lines	Patch %	Lines
crm/install.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2832      +/-   ##
===========================================
+ Coverage    71.18%   71.29%   +0.10%     
===========================================
  Files          175      176       +1     
  Lines        12360    12410      +50     
===========================================
+ Hits          8799     8848      +49     
- Misses        3561     3562       +1     

Files with missing lines	Coverage Δ
crm/api/dashboard.py	90.54% <100.00%> (ø)
crm/fcrm/doctype/crm_deal/crm_deal.py	90.45% <100.00%> (+0.04%)	⬆️
.../fcrm/doctype/crm_organization/crm_organization.py	82.60% <100.00%> (+0.79%)	⬆️
crm/hooks.py	100.00% <100.00%> (ø)
crm/tests/test_default_currency.py	100.00% <100.00%> (ø)
crm/utils/__init__.py	94.77% <100.00%> (+0.06%)	⬆️
crm/install.py	16.66% <87.50%> (+3.07%)	⬆️

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