fix(resolve): avoid cloning snapshot nodes during resolution

[sunerpy]

Summary

• keep one canonical Arc<Node> per snapshot node and share it across name, file, kind, and id indexes
• add backward-compatible shared-node lookup methods to ResolutionContext and switch hot resolver, framework, import, and name-matching paths to them
• preserve deterministic candidate ordering and the existing Vec<Node> compatibility surface

Performance evidence

• focused resolution benchmark: 65.92s -> 4.60s wall time (14.3x faster), 773.71s -> 0.44s system CPU, and 5.47m -> 59k minor faults
• release binary cold codegraph init on /config/workspace/ProdDir/vscode: 13,568 files, 375,287 nodes, and 1,693,459 edges in 6m30.69s
• before/after graph exports were byte-identical (about 24 MiB)

Validation

• make ci
• cargo build --release -p codegraph-rs
• real VS Code cold index rebuild with the release binary

[codecov]

Codecov Report

❌ Patch coverage is 99.34426% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/codegraph-resolve/src/import_resolver.rs	95.91%	2 Missing ⚠️

@@           Coverage Diff            @@
##             main     #242    +/-   ##
========================================
  Coverage   95.36%   95.36%            
========================================
  Files         141      141            
  Lines       79452    79602   +150     
========================================
+ Hits        75767    75915   +148     
- Misses       3685     3687     +2     

Files with missing lines	Coverage Δ
crates/codegraph-resolve/src/context.rs	98.58% <100.00%> (+0.10%)	⬆️
crates/codegraph-resolve/src/frameworks/godot.rs	87.69% <100.00%> (+0.10%)	⬆️
crates/codegraph-resolve/src/frameworks/nestjs.rs	98.99% <100.00%> (ø)
crates/codegraph-resolve/src/frameworks/react.rs	95.00% <100.00%> (ø)
crates/codegraph-resolve/src/frameworks/tauri.rs	93.17% <100.00%> (ø)
crates/codegraph-resolve/src/frameworks/vue.rs	99.35% <100.00%> (ø)
crates/codegraph-resolve/src/name_matcher.rs	97.59% <100.00%> (+<0.01%)	⬆️
crates/codegraph-resolve/src/resolver.rs	97.14% <100.00%> (+<0.01%)	⬆️
crates/codegraph-resolve/src/snapshot_context.rs	98.02% <100.00%> (+0.17%)	⬆️
crates/codegraph-resolve/src/types.rs	100.00% <100.00%> (ø)
... and 1 more

... and 2 files with indirect coverage changes

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