Fix line colors in map

[cchwala]

closes #18 but goes a bit beyond that (some more things were required along the way)

This PR does the following:

• Performance: Optimize CML map coloring by precalculating statistics in cml_stats table (~2.8s response time vs. 60s+ before)
• Database: Add cml_stats table and update_cml_stats() function to cache per-CML aggregations; parser updates cache on data insertion
• API: Refactor /api/cml-stats endpoint to use cached statistics with dynamic 60-minute stddev calculation
• Fix: Enable Grafana dashboard URL synchronization for CML selection (map clicks now update time series)
• Testing: Add unit tests for DB writer rollback behavior and API endpoint; fix import-time directory creation to support CI environments

[codecov]

Codecov Report

❌ Patch coverage is 80.95238% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.40%. Comparing base (9f3bd73) to head (a663359).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
parser/db_writer.py	70.00%	12 Missing ⚠️
webserver/main.py	66.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
+ Coverage   68.72%   73.40%   +4.68%     
==========================================
  Files          22       22              
  Lines        1848     1914      +66     
==========================================
+ Hits         1270     1405     +135     
+ Misses        578      509      -69     

Flag	Coverage Δ
mno_simulator	87.87% <ø> (ø)
parser	81.21% <83.33%> (+0.64%)	⬆️
webserver	44.73% <66.66%> (+15.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.