[ENHANCEMENT] Add interface, terminal, editor font size and spacing settings #2222

Problem (one or two sentences)

The chat text, code, terminal output, and row spacing of Zoo Code are fixed. Users who find the chat too small, too large, or too dense cannot change it.

Context (who is affected and when)

• Users on high-resolution or small screens who need larger text.
• Users who want a denser chat so that more fits on screen.
• Users who want terminal output and code blocks to use a different size from the chat text.

Checked against main: only the chat font size can be changed. Interface scale, terminal size, editor size, and spacing cannot.

Desired behavior (conceptual, not technical)

• UI tab: size steppers for Interface font size (%), Terminal font size (px), Editor font size (px), and Spacing density (%), each with a reset.
• A live preview that follows the steppers before the user presses Save.
• A value that is not set keeps the current look. A reset value goes back to the current look at once, also in the preview.

Constraints / preferences

• With nothing set, the layout and the sizes of code, diff, and terminal blocks stay exactly as they are.
• Values are limited to a safe range (50-200% and 8-32 px).
• The steppers use the keyboard and show the current value to assistive technology.
• New strings are translated in all supported locales.

Acceptance criteria

Given the user sets the terminal size to 18 px and presses Save,
Then command output in the chat uses 18 px.

Given the user clears a value,
Then the preview and the chat go back to the default size.

Given the user sets no value,
Then code, diff, and terminal blocks keep their current size.