Add Ruby examples to Learn, reference, and overview pages

[Aryex]

Summary

Add documentations for Ruby client 1.0.0 release and covers:

• Homepage
• Overview
• Learn section
• Reference section

Issue link

#300

Content Changes

• Getting Started: quickstart, basic-operations — Ruby tabs for
  install, standalone/cluster connection, and basic command examples.
• Core Features (concepts): batch-commands, custom-commands,
  valkey-scripting — Ruby tabs for pipelining/transactions, call/call_v,
  and scripting.
• Reference: connection-options (Ruby option mapping), scripting-reference
• Troubleshooting: Ruby tab for the connection-timeout example.
• Shared:
  • supported-languages-buttons
  • New Ruby button
  • astro.config.mjs
  • Ruby entry in the API References sidebar;
  • AGENTS.md Ruby in the supported-languages table plus language-tabs authoring guidance.

Testing

• pnpm build runs successfully (110 pages, internal links validated).
• pnpm format applied.
• All added Ruby snippets executed against the real 1.0.0.pre.rc2 gem.
• Visual review of the language buttons on the homepage.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one issue.
• Commit message has a detailed description of what changed and why.
• All commits are signed off with --signoff flag.
• pnpm build runs successfully.
• Links have been checked for validity.
• Destination branch is correct - main or release
• Create merge commit if merging release branch into main, squash otherwise.

[currantw]

Reviewed to 27b196d.

[Aryex]

@currantw I have removed the unnecessary comments.

On the Ruby scripting examples. I decided to remove them. The existing docs is about using the Script class which is a GLIDE interface not implemented in Ruby yet. Added valkey-io/valkey-glide-ruby#206 to track this.

[currantw]

Reviewed to adf96e0.
A few remaining comments.

[currantw]

Looks good ✅