[Midtown !5] Tighten code-author finishing checklist

[btucker]

Summary

• Add explicit rule: when tests pass, do NOT stop — push and open a PR immediately
• Reframe PR Lifecycle section as PR Lifecycle (Mandatory — every task ends with a PR) with an unambiguous opening statement
• Addresses the pattern of workers going idle after tests pass without pushing/creating a PR

Test plan

• Review agent definition changes in agents/definitions/midtown-code-author.md
• Verify new Task Execution rule clearly states tests passing is not completion
• Verify PR Lifecycle section heading and intro reinforce mandatory PR requirement

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.97%. Comparing base (05897b0) to head (7ba1087).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2335      +/-   ##
==========================================
+ Coverage   63.70%   63.97%   +0.27%     
==========================================
  Files         100      100              
  Lines       38582    38592      +10     
==========================================
+ Hits        24578    24690     +112     
+ Misses      14004    13902     -102     

see 10 files with indirect coverage changes

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