IDs, keys and prompt diffs line up in a monospace face

Text that is meant to be read character by character now looks like it, on the platform, in the console and in the assistant.

• Monospace where it matters. Record IDs, keys and other code-like values render in Geist Mono instead of the body font, so similar strings are easier to tell apart and copy.
• Prompt diffs that line up. In the console, each line of a prompt comparison keeps its indentation and spacing, so added and removed lines are easier to read against each other.
• The wordmark in its own face. The Sustentus wordmark now renders in the Sustentus typeface wherever it appears.

Nothing else changes: body text stays in the same typeface as before.