other: clean up help text spacing + help text dialog sizing

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

This PR fixes some text spacing with the help text dialog, and also does better width calculations to avoid multi-line unless necessary.

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.81%. Comparing base (d32b503) to head (82a4098).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/canvas.rs	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1865      +/-   ##
==========================================
+ Coverage   36.71%   42.81%   +6.09%     
==========================================
  Files         115      115              
  Lines       16096    16096              
==========================================
+ Hits         5910     6891     +981     
+ Misses      10186     9205     -981     

Flag	Coverage Δ
macos-14	37.98% <0.00%> (ø)
ubuntu-latest	44.32% <0.00%> (+6.39%)	⬆️
windows-2022	38.33% <0.00%> (ø)

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[Copilot]

Pull Request Overview

This PR improves the help dialog's visual presentation by standardizing text spacing and implementing dynamic width calculations to minimize unnecessary text wrapping.

Key Changes:

• Consolidated multi-line help entries and aligned spacing to 20 characters between keybindings and descriptions
• Implemented compile-time calculation of maximum text length for optimal dialog sizing
• Added dynamic width adjustment logic that centers the dialog with proper margins when space permits

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/constants.rs	Standardized help text spacing across all sections and reduced GENERAL_HELP_TEXT array from 32 to 28 entries by consolidating multi-line keybindings
src/canvas.rs	Added MAX_TEXT_LENGTH const computation and improved dialog width calculation using Flex::SpaceAround for better centering with margin handling

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