feat(docs): add offline examples reference

[Robinzon100]

docs: add docs/all_examples.md as offline feature reference

Motivation

During the recent website outage (#4869), the examples page at tabulator.info was unreachable. With no offline reference available, the only options were digging through source code or relying on external tools, neither ideal when you need to move fast.

What this adds

• docs/all_examples.md — a Markdown mirror of the website's examples page, organized by feature
• All deep-dive links still point to the original docs; this is intended as a quick-reference index, not a replacement
• Keeps everything self-contained inside the repo so the GitHub page can serve as a fallback during outages

Notes

• Content parity with the website's examples page as of this PR, no additions or omissions
• If this direction is welcome, I'm happy to expand the docs further so the repo can serve as a standalone reference

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This is my first open source contribution
feedback on structure or conventions is very welcome.