feat: add immutable scenes and upgrade the Node Flow site

[pavanpodila]

Summary

• add a renderer-facing immutable scene snapshot and coalesced scene deltas while preserving the existing controller, node builder, and MobX APIs
• retain per-node pictures for dense scenes, promote live/editing/dragging nodes to widgets, and make adaptive LOD opt-in so full detail remains the default at every zoom
• expand the release SkWasm benchmark to 500 and 1,000 nodes with a 16.67 ms / 60 FPS budget
• upgrade direct Dart, Flutter, and website dependencies to their newest resolvable versions
• version vyuh_node_flow as 0.32.0 through Melos and create the vyuh_node_flow-v0.32.0 release tag
• refresh the website, add the community carousel with Vyuh Workflow Editor first, remove per-card submission CTAs, and improve Pro CTA contrast
• add a focused test:core lane without deleting the fast full behavioral suite

Release WASM benchmark

500 nodes, retained renderer, p95 total frame time:

Scenario	p95	Frames over 16.67 ms
Pan	10.47 ms	0 / 60
Zoom	11.27 ms	0 / 59
Drag	9.58 ms	1 / 60
Churn	16.51 ms	2 / 59

At 1,000 nodes the retained pipeline improves the prior p95 results materially (for example, pan 31.41 -> 18.97 ms and churn 46.27 -> 31.21 ms), but topology churn and the largest scenes do not yet sustain 60 FPS consistently.

Validation

• dart analyze — clean
• full vyuh_node_flow suite — 6,926 passed, 0 skipped, 0 errors (22.4 s)
• focused renderer tests — passed
• pnpm build — passed (existing bundle-size advisory remains)
• release flutter run -d web-server --release --wasm — built and verified at http://localhost:8080
• browser smoke test — graph rendered with no console warnings or errors

[codecov]

Codecov Report

❌ Patch coverage is 89.74359% with 48 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.32%. Comparing base (66af32b) to head (6c064f7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ib/src/editor/controller/scene_projection_api.dart	78.31%	36 Missing ⚠️
...w/lib/src/editor/layers/nodes_thumbnail_layer.dart	90.00%	11 Missing ⚠️
...uh_node_flow/lib/src/editor/scene/graph_scene.dart	99.32%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
- Coverage   90.32%   90.32%   -0.01%     
==========================================
  Files         143      145       +2     
  Lines       10322    10775     +453     
==========================================
+ Hits         9323     9732     +409     
- Misses        999     1043      +44     

Flag	Coverage Δ
unittests	90.32% <89.74%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
...vyuh_node_flow/lib/src/connections/connection.dart	79.37% <100.00%> (+2.61%)	⬆️
...ib/src/editor/controller/node_flow_controller.dart	93.42% <100.00%> (+0.04%)	⬆️
...h_node_flow/lib/src/editor/layers/nodes_layer.dart	90.24% <100.00%> (+0.50%)	⬆️
...yuh_node_flow/lib/src/editor/node_flow_config.dart	100.00% <ø> (ø)
packages/vyuh_node_flow/lib/src/nodes/node.dart	99.30% <100.00%> (+0.09%)	⬆️
...s/vyuh_node_flow/lib/src/nodes/node_container.dart	82.97% <100.00%> (ø)
...vyuh_node_flow/lib/src/plugins/lod/lod_plugin.dart	98.00% <ø> (ø)
...uh_node_flow/lib/src/editor/scene/graph_scene.dart	99.32% <99.32%> (ø)
...w/lib/src/editor/layers/nodes_thumbnail_layer.dart	90.55% <90.00%> (+0.16%)	⬆️
...ib/src/editor/controller/scene_projection_api.dart	78.31% <78.31%> (ø)

... and 1 file with indirect coverage changes

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