feat(agents): inject current date into prompt context

[shunk031]

Motivation

Make the current local date and time available to both agent workflows at prompt submission time, so progress reports can use a fresh timestamp.

Changes

• Add a shared ~/.agents/date_context.py hook that emits the local timestamp in ISO 8601 format.
• Wire the hook into Claude Code's UserPromptSubmit event.
• Add the chezmoi symlink template for the shared hook.

Testing

• make setup
• Hook output smoke check for the event name, ISO 8601 timestamp, and first-prompt start-time guidance
• JSON parsing
• Python syntax and AST checks
• git diff --check
• chezmoi source mapping validation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.22%. Comparing base (58fcdfe) to head (aa15274).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #774      +/-   ##
==========================================
+ Coverage   80.86%   81.22%   +0.35%     
==========================================
  Files          25       25              
  Lines        1113     1113              
==========================================
+ Hits          900      904       +4     
+ Misses        213      209       -4     

Flag	Coverage Δ
macos	41.66% <ø> (ø)
rockylinux	80.63% <ø> (-0.35%)	⬇️
ubuntu	79.87% <ø> (+1.00%)	⬆️

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