fix: scoped init, select re-init, iOS zoom, command UX, checkbox indeterminate

[social5h3ll]

Combines 4 open PRs into one reviewable PR:

#151 (partial) - Scoped re-initialization + select fix

• Adds window.basecoat.initIn(container, options?) for scoped/partial DOM initialization
• Fixes select component re-init issue where event listeners weren't cleaned up
• Critical for htmx/Turbo/Unpoly users

#153 - Checkbox :indeterminate support

• Adds --indeterminate-icon CSS variable
• Styles :indeterminate state on checkboxes

#139 - iOS auto-zoom fix

• Changes select and combobox inputs from text-sm to text-base md:text-sm
• Prevents iOS from auto-zooming on input focus (16px threshold)

#136 - Command input text selection on re-open

• Auto-selects input text when command dialog opens
• Makes re-invoking command palette actually useful (existing text doesn't block new typing)

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Closes #151 (partially), #153, #139, #136

[social5h3ll]

Closing in favor of separate PRs per fix