Add automatic data retention/cleanup feature

[mircealungu]

Summary

• Add DATA_RETENTION_DAYS config option to automatically clean up old request data
• Default retention is 30 days (set to 0 to disable)
• Cleanup runs daily at 2 AM via APScheduler background job
• Uses efficient batch deletes instead of per-row iteration for better performance on large tables

Problem

The FMD database grows unbounded over time, causing slow startup (15+ seconds when tables have millions of rows):

• StackLine table: 16GB, 289M rows
• Request table: 97MB, 1.6M rows
• Outlier table: 274MB, 47K rows

Solution

Add a config option for data retention:

[database]
DATA_RETENTION_DAYS=30    # Keep 30 days of data (default)
DATA_RETENTION_DAYS=0     # Disable automatic cleanup
DATA_RETENTION_DAYS=90    # Keep 90 days

When DATA_RETENTION_DAYS > 0, cleanup is automatically scheduled on dashboard.bind(app).

Changes

• flask_monitoringdashboard/core/config/__init__.py - Add config option
• flask_monitoringdashboard/core/database_pruning.py - Add batch delete function and scheduler
• flask_monitoringdashboard/__init__.py - Auto-schedule cleanup in bind()
• config.cfg - Add example config
• tests/unit/core/test_database_pruning.py - New test file (6 tests)
• tests/unit/core/config/test_config.py - Add config parsing tests (3 tests)

Test plan

• Run existing unit tests - all 88 tests pass
• Test old requests are deleted while recent ones are preserved
• Test related records (Outlier, StackLine, ExceptionOccurrence) are cascaded
• Test orphan cleanup works correctly
• Manual testing with real database

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.06173% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.97%. Comparing base (2a07170) to head (2eb83fd).

Files with missing lines	Patch %	Lines
flask_monitoringdashboard/__init__.py	0.00%	3 Missing ⚠️
flask_monitoringdashboard/core/database_pruning.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #545      +/-   ##
==========================================
+ Coverage   86.73%   86.97%   +0.23%     
==========================================
  Files         115      116       +1     
  Lines        3611     3692      +81     
==========================================
+ Hits         3132     3211      +79     
- Misses        479      481       +2     

Files with missing lines	Coverage Δ
flask_monitoringdashboard/core/config/__init__.py	82.22% <100.00%> (+0.40%)	⬆️
tests/unit/core/config/test_config.py	100.00% <100.00%> (ø)
tests/unit/core/test_database_pruning.py	100.00% <100.00%> (ø)
flask_monitoringdashboard/core/database_pruning.py	65.90% <92.30%> (+17.52%)	⬆️
flask_monitoringdashboard/__init__.py	69.81% <0.00%> (-4.19%)	⬇️

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