docs: add Hopper community LLM integration

[pavanyellow]

Summary

• add Hopper to the supported LLM services table as a community-maintained integration
• document installation, configuration, usage, metrics, and model selection
• add navigation and redirect entries for the Hopper reference page

Integration

• Repository: https://github.com/hopper-inc/pipecat-hopper
• Release: https://github.com/hopper-inc/pipecat-hopper/releases/tag/v0.1.0
• Package: pipecat-hopper
• Maintainer: Hopper

Validation

• Prettier passes on all changed files
• Mint broken-link validation passes on Node.js 24
• Integration CI passes on Python 3.11, 3.13, and 3.14 against minimum, locked, and latest Pipecat versions

Before marking ready

• Complete the PyPI trusted-publisher registration and verify pip install pipecat-hopper
• Add a 30–60 second real voice-agent demo link

This is intentionally a draft until those two publication requirements are complete.