feat(bench): add latency distribution chart with log-normal fit

[hubcio]

Benchmark reports lacked visibility into latency shape
beyond summary percentiles. Operators couldn't distinguish
bimodal distributions from skewed unimodal ones.

Compute per-group latency histograms (50 bins) with
log-normal PDF fit and P5/P50/P95/P99 scatter markers.
Wire them through report types, chart generation, and
the dashboard frontend as a new "Distribution" tab.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.66%. Comparing base (1ca37f1) to head (34a1e6f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2832   +/-   ##
=========================================
  Coverage     67.66%   67.66%           
  Complexity      708      708           
=========================================
  Files          1030     1030           
  Lines         83846    83846           
  Branches      60702    60703    +1     
=========================================
+ Hits          56734    56738    +4     
+ Misses        24763    24758    -5     
- Partials       2349     2350    +1     

Flag	Coverage Δ
rust	69.71% <ø> (+<0.01%)	⬆️

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see 7 files with indirect coverage changes

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[krishvishal]

LGTM.