docs: align ruby gem guides with current config behavior

[gildesmarais]

Summary

This updates the Ruby gem documentation on the website so the examples and command reference match the current gem behavior more closely.

What changed

• align the Ruby gem reference pages with the current CLI and config surface
• move paginated feed docs into the selectors reference
• turn guide and tutorial examples into complete, valid configs
• add short notes where runtime behavior is easy to misunderstand, especially for dynamic parameters, channel metadata, and custom HTTP requests

Commit slices

• docs(ruby-gem): align reference pages with current config surface
• docs(ruby-gem): make guides and tutorials use valid configs

Validation

• validated representative updated configs against the gem runtime with mise exec -- ruby -Ilib -rhtml2rss
• checked the rendered pages locally with Chrome MCP at http://localhost:4321

Notes

• left the untracked local examples/ directory out of the PR
• did not touch web application docs in this pass

[Copilot]

Pull request overview

Updates the Ruby gem documentation to better match the current CLI/config surface, with examples rewritten as complete, valid feed configs and selector pagination guidance consolidated into the selectors reference.

Changes:

• Reworks CLI and reference pages to reflect current commands/config structure (e.g., schema, validate, top-level strategy).
• Moves/expands pagination documentation into the selectors reference and documents expected behavior.
• Updates guides/tutorials to use complete, valid YAML configs (and modernizes examples like HTTPS + JSON selector shapes).

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/content/docs/ruby-gem/tutorials/your-first-feed.mdx	Simplifies the selectors tutorial example and makes the config more realistic/complete.
src/content/docs/ruby-gem/reference/stylesheets.mdx	Makes the stylesheet example a full feed config (channel + selectors included).
src/content/docs/ruby-gem/reference/strategy.mdx	Clarifies top-level strategy placement and updates CLI usage examples.
src/content/docs/ruby-gem/reference/selectors.mdx	Adds a dedicated “Paginated Feeds” section with config and behavior notes.
src/content/docs/ruby-gem/reference/headers.mdx	Turns the headers snippet into a complete, valid feed config example.
src/content/docs/ruby-gem/reference/cli-reference.mdx	Replaces the old CLI writeup with a clearer command-oriented reference (auto/feed/schema/validate/help/version).
src/content/docs/ruby-gem/reference/channel.mdx	Provides a complete channel-in-context example plus runtime notes for common pitfalls.
src/content/docs/ruby-gem/reference/auto-source.mdx	Ensures examples include channel.url context for valid configs.
src/content/docs/ruby-gem/how-to/scraping-json.mdx	Updates examples to HTTPS and includes required selectors (items, title, url).
src/content/docs/ruby-gem/how-to/managing-feed-configs.mdx	Replaces placeholder selector blocks with concrete, valid per-feed examples.
src/content/docs/ruby-gem/how-to/dynamic-parameters.mdx	Updates the example to a complete config and adds clarifying notes about parameterization scope.
src/content/docs/ruby-gem/how-to/custom-http-requests.mdx	Makes all header examples complete configs and aligns dynamic header placeholders to %<param>s.
src/content/docs/ruby-gem/how-to/advanced-features.mdx	Updates examples to include required channel/url selectors so snippets are valid configs.