SCIX-890 fix(vis): keep paper limit and CSV reachable on empty network

[thostetler]

The author and paper network pages dropped the entire graph pane when the
backend couldn't build groups, so a user who over-restricted the paper limit
had no way to raise it back and nothing to export. The "not enough data"
response also uses a different shape than success (no root/summaryGraph; raw
rows under fullGraph), which the CSV path wasn't reading.

1. Add a shared NotEnoughData panel that keeps the paper limit control on
   screen and offers an optional CSV download.
2. Build the error-state CSV from fullGraph.nodes (author name and weight;
   paper bibcode and metadata), omitting the button when there are no rows.
3. Model the fullGraph fallback in the vis response types.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.6%. Comparing base (7872cc8) to head (f16e274).

Files with missing lines	Patch %	Lines
...izations/Containers/AuthorNetworkPageContainer.tsx	18.8%	13 Missing ⚠️
...lizations/Containers/PaperNetworkPageContainer.tsx	38.1%	13 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #905     +/-   ##
========================================
+ Coverage    67.4%   67.6%   +0.3%     
========================================
  Files         349     350      +1     
  Lines       41238   41334     +96     
  Branches     2132    2137      +5     
========================================
+ Hits        27762   27912    +150     
+ Misses      13427   13373     -54     
  Partials       49      49             

Files with missing lines	Coverage Δ
...ts/Visualizations/Widgets/NetworkNotEnoughData.tsx	100.0% <100.0%> (ø)
src/components/Visualizations/Widgets/index.ts	100.0% <100.0%> (ø)
src/components/Visualizations/utils/graphUtils.ts	59.5% <100.0%> (+1.5%)	⬆️
...izations/Containers/AuthorNetworkPageContainer.tsx	20.5% <18.8%> (-0.8%)	⬇️
...lizations/Containers/PaperNetworkPageContainer.tsx	23.1% <38.1%> (+0.4%)	⬆️

... and 7 files with indirect coverage changes

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