feat: compute the jacobian analytically

[lpatiny]

Also stops optimize from mutating the peaks it receives, aligns tooling with current standards, fixes the README example and reworks the web demo.

Sum of gaussians, 1024 points
numerical -> analytical (ms):

• 1 peak 15.2->21.8
• 3 peaks 63.2->37.4
• 5 peaks 138.7->57.0
• 10 peaks 522.1->127.2
• 20 peaks 1965.8->352.8
• 10 pseudoVoigt 823.0->208.1

Fitted parameters unchanged. Only pays off from ~2 peaks: for a single one the per-point derivative allocations cost more than 3 model evaluations.

Assisted-By: Claude Opus 5 (1M context) noreply@anthropic.com

[codecov]

Codecov Report

❌ Patch coverage is 91.20879% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.85%. Comparing base (e5d13e7) to head (369786f).

Files with missing lines	Patch %	Lines
src/util/internalPeaks/DefaultParameters.ts	78.37%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
+ Coverage   97.54%   97.85%   +0.31%     
==========================================
  Files          11       13       +2     
  Lines         366      420      +54     
  Branches       71       73       +2     
==========================================
+ Hits          357      411      +54     
  Misses          9        9              

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[jobo322]

The changes look fine, and also fix a side effect