Add label to search input

[ckundo]

Fixes #51

Changes

• ✅ Add <label> element associated with search input via htmlFor/id
• ✅ Add aria-describedby for additional search context
• ✅ Use .sr-only class to hide label visually
• ✅ Provide helpful description of searchable fields
• ✅ Add .sr-only utility class to CSS

WCAG Compliance

3.3.2 Labels or Instructions (Level A) - Labels must be provided for inputs
4.1.2 Name, Role, Value (Level A) - Form elements must have accessible names

Before & After

Before: Input with only placeholder text (not accessible to screen readers when focused)
After: Input with proper <label> and descriptive help text

Screen Reader Experience

When focusing the search input, screen readers will announce:

• "Search builds, edit text"
• "Search by build ID, branch name, commit hash, or triggered by"

Testing

• Build succeeds
• Screen reader announces label when focusing input
• Screen reader announces help text
• Label visually hidden but programmatically available
• Search functionality unchanged