Revert <wa-code-demo> in docs

[claviska]

The <wa-code-demo> component is marked as experimental but it's way too opinionated and messy for a stable candidate. It was an opportunistic addition that was added hastily and it's made it more difficult to fix things like #680 due to the abstracted logic.

It also introduced problems with <wa-popup> being clipped/sized problematically in various demos like dropdown, select, and other popup-related components.

There may be value in such a component at some point, but at the moment it's easier to revert to the old behavior and inline the examples.

@lindsaym-fa I brought back the original resizer and made it even better than the tiny handle we have now.

CleanShot.2025-05-21.at.16.32.48.mp4

This PR also fixes #680.

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TODO

• The <wa-page> docs are borked because they're not isolated anymore. I may move these to separate windows unless @KonnorRogers has another idea for them.
• Normalize a handful of camelCased filenames
• Review remaining docs to ensure everything is working as expected

Note: There are some spacing issues in various places as a result of this change, which appear to be from the ridiculously high specificity of the native style selectors, so most of that should be fixed with #943 and the addition of CSS layers., e.g.:

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[claviska]

I fixed the <wa-page> docs by breaking out the two demos into separate HTML files. This works nicely, as the user can view and inspect full-sized pages now.