refactor(web): remove prompt generator React.FC

[lyzno1]

Summary

• type PromptGeneratorBtn props directly on the function parameter
• remove the FC type import and annotation
• preserve the component API, JSX, state transition, and runtime behavior

Dependency

This cleanup is stacked on #40329 only because it edits the same component after the icon conversion. It has no accessibility or runtime dependency and remains a separate review layer.

Visual regression review

This is a type-only refactor. The emitted JSX, classes, visible content, interaction states, modal behavior, and accessibility tree are unchanged. A visual difference would be a regression.

Validation

• focused Vitest: 1/1 passed
• standalone accessibility lint: 0 findings
• focused format/lint/type check: 0 findings
• full pnpm check: 0 errors, 2058 existing warnings
• git diff --check: passed

Rollback

Revert this PR alone to restore React.FC without affecting either lower stack layer.

[lyzno1]

Closing during the accessibility stack audit. This layer only changes component typing or icon implementation, adds no user-visible accessibility contract, and carries independent visual/review risk. It can be reconsidered later as a separate cleanup, not as an a11y dependency.