Convert docs from MkDocs/Material to Astro Starlight

[Copilot]

• Remove stale docs/theme_overrides gitlink that caused CI submodule fetch failure
• Add K2D (weight 400) font with mylonics gray color to .site-title span and .hero h1 in docs/src/styles/custom.css

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[rijesha]

@copilot
Run actions/checkout@v4
Syncing repository: mylonics/struct-frame
Getting Git version info
Temporarily overriding HOME='/home/runner/work/_temp/9622390e-3aaa-44d7-a7bb-12a9a20c58d6' before making global git config changes
Adding repository directory to the temporary git global config as a safe directory
/usr/bin/git config --global --add safe.directory /home/runner/work/struct-frame/struct-frame
Deleting the contents of '/home/runner/work/struct-frame/struct-frame'
Initializing the repository
Disabling automatic garbage collection
Setting up auth
Fetching the repository
Determining the checkout info
/usr/bin/git sparse-checkout disable
/usr/bin/git config --local --unset-all extensions.worktreeConfig
Checking out the ref
Setting up auth for fetching submodules
Fetching submodules
/usr/bin/git submodule sync
/usr/bin/git -c protocol.version=2 submodule update --init --force --depth=1
Error: fatal: No url found for submodule path 'docs/theme_overrides' in .gitmodules
Error: The process '/usr/bin/git' failed with exit code 128

Also ensure main page struct-frame title is in mylonics gray and 400 weight k2d font in the both the title bar and the main page text.

[rijesha]

@copilot try again

[rijesha]

@copilot try again

[Copilot]

@copilot try again

Fixed in commit 1b647cf:

1. CI fix: Removed the stale docs/theme_overrides gitlink (mode 160000) that had no .gitmodules entry — this was the root cause of the fatal: No url found for submodule path 'docs/theme_overrides' error.

2. Title styling: Added K2D font (weight 400) with mylonics gray to both the site title bar and the hero heading in docs/src/styles/custom.css:

   • Dark mode: #adb5bd (ml-gray-400)
   • Light mode: #555555 (ml-gray-600)
   • Targets .site-title span and .hero h1