Show which runtime each browser page uses and run at full speed by default

[sacckey]

Summary

• Open the browser version without the 60 FPS limit by default, so the FPS display shows how fast each runtime is. ?throttle=1 keeps the old behavior.
• Add a Runtime section to both pages that shows whether the page runs on ruby.wasm or Spinel and links to the other one.
• Put the runtime in the page title: Ruby Boy (ruby.wasm) and Ruby Boy (Spinel).
• Update the playback options in wasm/README.md.

Only the pages under docs/ change, so the Wasm files in the v1.7.0 release do not need to be rebuilt.

Test plan

• Both pages load, run Tobu Tobu Girl and link to each other
• The selected runtime and the hover state are readable (text contrast 5.9:1 or higher)
• After the Pages deploy, check in a foreground browser window that the FPS goes above 60 by default

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