fix: display dynamic help shortcut hint based on focus

[linw1995]

Summary

Fix duplicate help shortcut hints by showing the appropriate key based on current focus state:

• Input focused: Display Esc+? (require blur first)
• Other focus: Display ? directly

Changes

• Update decorate_block_top signature to accept is_input_focused parameter
• Remove hardcoded help hint from input component
• Dynamically render help key in shortcut hints panel based on focus state

Impact

• coco-tui shortcut hints panel

Fixes duplicate hints and makes help guidance more accurate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.58%. Comparing base (a46f02c) to head (9c5653c).
⚠️ Report is 16 commits behind head on dev.

Files with missing lines	Patch %	Lines
crates/coco-tui/src/components/shortcut_hints.rs	0.00%	10 Missing ⚠️
crates/coco-tui/src/components/chat.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #160      +/-   ##
==========================================
- Coverage   50.22%   47.58%   -2.65%     
==========================================
  Files          93      100       +7     
  Lines       25033    27316    +2283     
==========================================
+ Hits        12574    12999     +425     
- Misses      12459    14317    +1858     

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