[codex] Add proptest coverage

[glslang]

Summary

• add proptest as a test-only dependency for the Rust core and bridge crates
• add property coverage for accepted event inputs, UHK macro command sizing, and report framing
• add bridge IPC property coverage for JSON-line request/response round-trips and arbitrary raw-frame decode/error behavior

Verification

• cargo test -p agent-notify-core
• cargo test -p agent-notify-bridge
• cargo fmt --all
• cargo test --workspace

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.44%. Comparing base (ee09a6b) to head (660bb1e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   63.35%   66.44%   +3.08%     
==========================================
  Files          12       12              
  Lines        1411     1517     +106     
==========================================
+ Hits          894     1008     +114     
+ Misses        517      509       -8     

Flag	Coverage Δ
rust	66.44% <100.00%> (+3.08%)	⬆️

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

Files with missing lines	Coverage Δ
crates/agent-notify-bridge/src/ipc.rs	98.71% <100.00%> (+1.04%)	⬆️
crates/agent-notify-core/src/lib.rs	88.99% <100.00%> (+4.38%)	⬆️

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