SEO: Canonical links need to be added

[Deykun]

Recently, a sitemap has been added for the project, and I have been able to check the report for this app.

The majority of mismatches result from indexing r= as a separate page (these results are shared by players).

Results for a language should have one canonical.

Since the "About the language" page (ex. https://deykun.github.io/diffle-lang/en?p=about-language ) also uses GET parameters and I want to index it as an individual subpage, and I cannot do SSR with GitHub Pages en/info or en-about should be created for it.

[Deykun]

As part of it, I had to test support for a custom path.

• 🧭 Router: testing github 404 #158
• 🧭 Router: testing github 404 end #159

It works.

[Deykun]

Current state: