feat: add coco tell command and simplify coco ask semantics

[linw1995]

• Introduce coco tell command for sending prompts without waiting for replies
• Simplify coco ask to always expect a reply, removing the --reply flag
• Add default schema handling: when no schemas provided, defaults to message field and prints only the message string
• Refactor ask.rs into prompt.rs with unified prompt resolution logic
• Update TUI client to support both ask and tell commands
• Update existing combos and tests to use new command semantics
• Maintain backward compatibility for existing schemas usage

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.51748% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.25%. Comparing base (fad69e0) to head (003199b).
⚠️ Report is 8 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/cmd/prompt.rs	81.88%	23 Missing ⚠️
src/main.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##              dev      #77    +/-   ##
========================================
  Coverage   59.25%   59.25%            
========================================
  Files          77       77            
  Lines       15488    15865   +377     
========================================
+ Hits         9177     9401   +224     
- Misses       6311     6464   +153     

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