[tempus2016]

Fixes #1078

The setup wizard showed a colour picker for each child but never saved the choice, and the Children dialog had no colour field. The panel always coloured children by their position in the list, using a different palette from the one the wizard showed.

Changes

• Model: Child.color — "#rrggbb", or "" for the automatic colour. Children saved before this read as "", so nothing changes for them.
• Validation: add_child, update_child and setup_wizard/apply only accept a #rrggbb hex value (saved lowercase) or empty. Strict, because the panel puts it into a style attribute.
• Wizard: sends the colour it shows when it creates a child.
• Edit child dialog: a Colour row with an Automatic swatch (the current position-based colour) plus the wizard's 8 colours.
• Panel: _childColor() uses the stored colour and falls back to the old palette. It now also colours the avatar on the Children tab, so a new pick is visible straight away.
• New strings in all 10 locales.

Out of scope: Lovelace cards still use their own header_color option.

Testing

• tests/test_child_color.py: model round-trip, validator (accepts / lowercases / rejects #fff, red, style injection), wizard save, add, update, and clear. Full suite: 3256 passed. Ruff, ESLint, translation and data-file checks all pass.
• ha-dev: through the real panel, set Vaiha to purple → saved, the dialog reopens with it selected after a reload, and the Children tab avatar, Today card and child picker all use it. No console errors. A WebSocket probe confirmed storage, the invalid_format rejection, that the colour is kept when other fields are saved, and clearing. A setup_wizard/apply probe confirmed the wizard's colour is stored (probe child removed afterwards).