docs: build out the CAST PRO-1 section - #1207

What does this implement/fix?

Builds out the CAST PRO-1 section for launch, modeled on the CAST-1 section. Before this PR the section only had an Introduction and an LED strip page.

New pages

• FAQ
• Getting Started: labeled ports photo and table, USB-C power (5V 1A, or 5V 3A with an LED strip), speaker hookup clip, Ethernet / hotspot / Improv setup with a hotspot onboarding clip, Audio Output, and Music Assistant
• Additional Info: Sensor Definitions (matched to the real device page), ESPHome Device Builder, and Analog In (playing the line-in source from Music Assistant Browse as a Sendspin Source, plus the Line In Streaming options)
• Examples: TTS and Announcements, WizMote Control
• Troubleshooting: Boot Mode, Reflash, Status Check and Factory Reset (3 second hold shows connection status on the LEDs, 10 second hold factory resets), and Teardown and Reassembly with clips

Updated pages

• Introduction: hero image, and the features rewritten for the actual hardware
• LED Strip: screw terminal order, the LED Strip Test step, Effect A and Effect B slots with the pattern list and photosensitivity warning (from the CAST-1 README), and a partition example for splitting the strip into segments (based on the Halloween example YAML)

Style guide and AGENTS.md: adds a naming rule for CAST PRO-1: display text never says CAST-1 PRO, and the literal device name and hotspot keep CAST_PRO-1 (Apollo CAST_PRO-1 Hotspot).

Media: 10 new WebP assets in docs/assets/cast-pro-1-*, all under 1.5 MB. The hotspot onboarding clip was cut from a phone screen recording: other Wi-Fi networks, the keyboard, browser search suggestions, a password manager prompt and the password characters are cut or masked, and I checked every frame. The photos have no location data.

Notes for reviewers

• Two TODO comments remain, hidden in the rendered pages:
  • The firmware option name in the installer dialog, on the Reflash page.
  • Whether the CAST-1 WizMote blueprint lists CAST PRO-1 devices.
• The Analog In page has a placeholder comment for a Music Assistant screenshot.
• No redirects are needed. None of the moved or renamed pages were ever on dev.
• check_markdown, check_secrets and check_links pass locally on a full build. check_images couldn't run because exiftool isn't installed on my machine; the images were checked for location data with Pillow instead.

Types of changes

• Typo / wording fix
• Content update (correcting outdated info, adding missing steps, clarifications)
• New page or new product section
• Page move / rename (redirect added in mkdocs.yml)
• Image / screenshot update
• Nav / structure change
• Site config or theme change
• CI / workflows / dependencies — Does not publish

Checklist:

• This PR targets the dev branch (not main)
• Changes previewed locally with mkdocs serve
• If pages were moved or renamed, redirects were added to mkdocs.yml
• If new pages were added, nav was updated in mkdocs.yml

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