[FEATURE] UI Customization. Add control-size design tokens

[zhuje]

Description

Follow-up to the sizing question on #312. Adds a control-size scale to @perses-dev/design-tokens so controls of the same size share a height.

--perses-size-control-xs: 1.5rem; /* 24px */
--perses-size-control-sm: 2rem;   /* 32px */
--perses-size-control-md: 2.5rem; /* 40px */
--perses-size-control-lg: 3rem;   /* 48px */

• Tokens added to tokens.css, tokens.ts and types.ts, with tests.
• IconButton uses them for width and height (xs grows from 1rem to 1.5rem, which meets the WCAG 2.5.8 24px minimum target).
• Button uses them as min-height, so it grows with larger text instead of clipping. Box sizing is border-box via the reset, so the token is the outer height including the 1px border.
• Out of scope: Chip ([FEATURE] UI Customization. Add Chip primitive component #320, to rename its sizes to xs/sm), TextField ([FEATURE] UI Customization. Textfield Component #354), and an indicator scale for Checkbox/Switch/icons. These follow once this merges.

Visual changes to merged components: Button xs and sm grow by about 0.25rem, md and lg change by about 0.1rem, IconButton xs grows by 0.5rem.

Screenshots

Not included yet.

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

UI Changes

• Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• Code follows the UI guidelines.
• E2E tests are stable and unlikely to be flaky.
  See e2e docs for more details.

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 41aaf1b.}