feat: dynamic banner resizing via bubbletea view

[srtaalej]

Changelog

Added an interactive shell mode with a styled welcome banner, bubbletea-powered input prompt, and command history navigation. 🦋

Summary

Move the shell banner into the bubbletea input model's View() so it responds to terminal resizes. The banner renders above the input on the first prompt only and disappears after the user submits a command.

Screen.Recording.2026-03-03.at.10.29.12.AM.mov

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.18%. Comparing base (c449532) to head (da9221d).

Files with missing lines	Patch %	Lines
cmd/shell/input.go	75.34%	17 Missing and 1 partial ⚠️
cmd/shell/shell.go	83.33%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
+ Coverage   65.06%   65.18%   +0.11%     
==========================================
  Files         215      218       +3     
  Lines       18179    18322     +143     
==========================================
+ Hits        11829    11943     +114     
- Misses       5254     5277      +23     
- Partials     1096     1102       +6     

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