docs: rewrite README and docs/ (includes a trademark question needing your decision)

[willtheorangeguy]

Rewrites the README, restructures docs/, and records three defects — the first of which needs a decision from you.

The licence position on the images. LICENSE.md is GPL v3 and the README said "This project is licensed under the GNU General Public License" with no carve-out. The three bundled GIFs are the Python logo and the two "Python Powered" badges — PSF trademarks, governed by the PSF Trademark Usage Policy, not the author's to place under GPL. The GPL grants recipients the right to modify and redistribute what it covers, which is exactly what a trademark policy restricts.

This is the one repository in the sweep whose entire content is third-party trademarked artwork, so it is not a corner case. The README now states the split — code GPL, images PSF — and the finding records three options (an explicit split in LICENSE.md, a NOTICE/CONTENT_LICENSE.md, or replacing the bundled marks with original artwork and linking the official badges). I changed no licence file; that is yours to decide.

README — the /blob/-free screenshots now come from the .github icons repo, ## Changelog and ## You may also like are gone, and the credits table is untouched.

docs/ restructured. CUSTOMIZATION.md and USAGE.md removed, their content folded into configuration.md and quickstart.md. docs/images/ removed. docs/legal/PRIVACY.md and TERMS.md lowercased to match the docs contract (README links updated). New: index, quickstart, installation, configuration, architecture, api, development, faq, troubleshooting, roadmap.

Also recorded:

• The privacy policy and terms describe a service this is not. Both are generated boilerplate dated August 2022, defining Account, Affiliate, and Personal Data, and opening "This Privacy Policy describes Our policies and procedures on the collection, use and disclosure of Your information when You use the Service." This package opens no connection, creates no account, and stores nothing. Boilerplate is worse than absence here — it makes a package that collects nothing look like one that collects something, and the README linked both from its License section.
• str(files(...)) assumes a filesystem path, so _load_image fails for a zipimported package. It is the last step of the importlib.resources reasoning left incomplete, and it fails in exactly the packaging scenario a widget library gets swept into — someone bundling their Tkinter app. as_file() is the fix.

Worth noting approvingly, and documented as such in architecture.md: resources are resolved through importlib.resources rather than a path relative to __file__ or the CWD, and each widget binds its PhotoImage to self._image. Those two are the difference between this package and the two sibling Tkinter repos in this batch, both of which get one or the other wrong and fail silently for it.

Documentation only — no source, image, or licence-file changes.