docs(scrollbar): improve API discovery

[joshka]

Summary

• Improve tui-scrollbar crate docs for API discovery, styling behavior, glyph selection, and interaction flow.
• Add a small scrollbar_styled example that shows distinct track, thumb, and arrow styles for vertical and horizontal scrollbars.
• Configure docs.rs example scraping and add a regression test for custom thumb styling on full and partial thumb cells.

Details

This is a non-functional docs/examples/tests change. It reorganizes the crate-level docs so important defaults and caveats are visible earlier, replaces the loose ScrollBar “Key methods” list with a grouped method map, and adds canonical examples for the main builder methods.

The styling docs now spell out how fg and bg apply to terminal glyph cells. In particular, they call out that the default minimal track renders spaces, so empty track cells show background color, while visible glyph sets can use foreground color for the track line. The docs also note the partial-thumb caveat: when using visible tracks such as GlyphSet::box_drawing, thumb background can show at partial glyph edges, so matching it to the track background is usually less surprising.

The glyph docs keep repeated Symbols for Legacy Computing context where readers may land directly, rather than relying on linear reading through the crate docs.

Related context:

• Issue Support styling for scrollbar widgets #193: Support styling for scrollbar widgets #193
• PR feat(scrollbar)!: WIP - Refactored and added scrollbar component style with defaults #201: feat(scrollbar)!: WIP - Refactored and added scrollbar component style with defaults #201

Validation

• cargo test -p tui-scrollbar --all-features
• cargo test -p tui-scrollbar --doc --all-features
• cargo check -p tui-scrollbar --examples --all-features
• cargo clippy -p tui-scrollbar --all-targets --all-features
• RUSTDOCFLAGS='-D warnings' cargo doc -p tui-scrollbar --no-deps --all-features
• just fmt-check
• cargo rdme --check --manifest-path tui-scrollbar/Cargo.toml
• markdownlint-cli2 tui-scrollbar/README.md

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.65%. Comparing base (2cd4955) to head (b63695d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #251      +/-   ##
==========================================
+ Coverage   87.57%   87.65%   +0.07%     
==========================================
  Files          22       22              
  Lines        4210     4237      +27     
==========================================
+ Hits         3687     3714      +27     
  Misses        523      523              

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[joshka]

@tremby happy to take a review on language here if anything is unclear. I'd recommend rendering locally to view the docs there directly rather than just diff checking

cargo doc -p tui-scrollbar --open 

[tremby]

I read through all of it, looks good to me. Seems clear. Thanks.

(Caveat: I can't comment on accuracy, and I didn't run the example code.)

[joshka]

I read through all of it, looks good to me. Seems clear. Thanks.

That's my bar on this sort of thing. Thanks for looking.