Split oversized frontend components

[gauthierpiarrette]

Problem
Three components exceed the 150-line guideline from the project coding standards:

• FormField.svelte — 316 lines
• ToolDetail.svelte — 352 lines
• ResultView.svelte — 325 lines

Large components are harder to review, test, and maintain.

Proposed solution

• ToolDetail → extract ToolHeader.svelte (name, badges, description, warnings) and InputModeSelector.svelte (form/json/schema tabs)
• FormField → extract ArrayField.svelte and UnionField.svelte (oneOf/anyOf handling)
• ResultView → extract TextResultBlock.svelte, ImageResultBlock.svelte, JsonResultBlock.svelte

Alternatives considered
Leaving as-is since they work. But smaller components are easier to unit test with Vitest and follow the project's own standards.