feat(studio): refine component library organization and interactions

[evanlowe]

Organize the Studio component catalog into Foundation, Base, Block, AI App, Node and Layout. Each component has a page title, variants use second-level headings, and desktop/mobile contents navigation preserves existing preview links.

• Standardize Button sizes, proportional icons, rounded icon buttons and size labels; remove conflicting consumer styles and reduce default Loading sizes
• Rebuild Progress as a left-aligned step title, looping loading bar and background-free ScrollArea, with upward title transitions and a stable completed state
• Animate new conversation steps by expanding their space before fading in the content, with reduced-motion and immediate interaction support
• Add a shared Foundation Specification for component/layout reuse, complete interactions, typography, motion, product copy and optical alignment
• Refresh the production WebUI assets and component documentation

Progress remains exported as LongRunningState. Its obsolete heading, selectedStep and onSelectedStepChange props are removed; the preview and tests use the updated API.

Validation:

• Frontend unit tests: 1,213 passed on Node 22
• Progress and ConversationFlow interaction tests: 17 passed
• Sidecar coverage gate: 22 passed, 98.55% statement coverage and 94.44% branch coverage
• Production build and asset verification: passed, including 113 packaged files and 350 internal references
• Pre-commit across all files, including secret scanning: passed
• Manual preview checks: desktop/mobile, light/dark, reduced motion, legacy links, button dimensions, and Volcengine/BytePlus layouts