docs(P6.4): repoint all doc links from the GitHub wiki to docs.wickra.org (#86)

The documentation now lives in the wickra-lib/wickra-docs VitePress repo and
will deploy to docs.wickra.org. Rewrite every tracked, user-facing wiki link
in the main repo to the new canonical site:

- docs/README.md, CONTRIBUTING.md, PULL_REQUEST_TEMPLATE.md
- bindings/{node,python,wasm}/README.md, examples/wasm/README.md
- repo-metadata.toml: wiki_url/wiki_git -> docs_url/docs_git

Page paths map 1:1 to VitePress clean URLs (e.g. /wiki/Quickstart-Rust.md ->
docs.wickra.org/Quickstart-Rust). The sync-about.yml wiki-sync step is left
untouched on purpose: it stays until the docs site is live (tracked as P8.3).
The GitHub wiki itself is not deleted yet for the same reason.

CONTRIBUTING.md

@@ -96,9 +96,9 @@ the repository root is not an npm package.
 - **Bindings.** A change to a public indicator API must be mirrored across the
   Python, Node, and WASM bindings, including their type stubs / `.d.ts`.
 - **Docs.** Update the relevant page on the
-  [project Wiki](https://github.com/wickra-lib/wickra/wiki) and the
-  `README.md` when behaviour or the public API changes. The Wiki lives in
-  a separate git repository: `https://github.com/wickra-lib/wickra.wiki.git`.
+  [documentation site](https://docs.wickra.org) and the
+  `README.md` when behaviour or the public API changes. The docs live in
+  a separate git repository: `https://github.com/wickra-lib/wickra-docs`.
 - **Changelog.** Add an entry under `## [Unreleased]` in `CHANGELOG.md`.
 
 ## Commit and pull-request workflow