Document sensor platform for Hot Spring

[Moustachauve]

Proposed change

This adds the documentation for the new sensor platform for Hotspring integration.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logos and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Add Hotspring sensor platform core#179697
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue: fixes #

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

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[Copilot]

Pull request overview

Documents the new Hot Spring sensor platform in Home Assistant.

Changes:

• Adds sensor metadata to the integration page.
• Documents temperature, salt-system, and firmware sensors.
• Notes availability and default-disabled entities.

Suppressed comments (3)

source/_integrations/hotspring.markdown:75

• Core only creates this entity when spa.versions.control_box is non-empty; its tests also cover the no-version case. As written, this says the entity is merely disabled, but on devices without a reported version it is absent. Please document that availability condition, as you do for the FreshWater sensor.

- **Control box version**
  - **Description**: Firmware version of the spa control box.
  - **Remarks**: Disabled by default.

source/_integrations/hotspring.markdown:81

• Core only creates this entity when spa.versions.wifi_dongle is non-empty; its tests also cover the no-version case. As written, this says the entity is merely disabled, but on devices without a reported version it is absent. Please document that availability condition.

- **Wi-Fi dongle version**
  - **Description**: Firmware version of the Wi-Fi dongle.
  - **Remarks**: Disabled by default.

source/_integrations/hotspring.markdown:66

• This availability note does not match the parent implementation's behavior: the three cartridge sensors are created only when cartridge_installed is true during platform setup, and that predicate is not re-evaluated on coordinator updates. Installing or removing a cartridge later therefore does not add or remove these entities (and removed cartridges can leave stale values). Please fix the parent implementation to track availability dynamically, or document that reloading the integration is required.

- **Salt 10-day check timer**
  - **Description**: Number of days remaining until the next 10-day salt water test reminder.
  - **Availability**: Available when a FreshWater Salt System cartridge is installed.

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[Moustachauve]

Done.