fix(dashboard): preserve input error focus - #7430

Summary

• keep red error border, focus ring, and hover border while an invalid dashboard input is active
• apply brand focus and hover colors only to inputs without an error
• add focused class-contract regressions for both states

Inventory finding: F-2c327f7cf9ff7043

Verification

• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard exec vitest run src/components/ui/Input.test.tsx (2 passed)
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard test (102 files, 1077 tests passed)
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard typecheck
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard lint
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard build
• git diff --check
• pre-commit and pre-push hooks

Out of scope

• changing input validation rules or error copy
• changing other form-control components
• broader design-system color changes