feat: add live character counter to InputField maxLength fields (Closes #1291)

[waterWang]

Summary

Adds an opt-in live character counter (42/100 style) to InputField fields that declare a maxLength prop, implementing issue #1291.

Changes

src/components/InputField.tsx

• Added maxLength prop to InputFieldProps — counter only renders when explicitly provided
• Counter reads the child <input>'s current value to derive charCount in real time
• Counter text is linked via aria-describedby on the input
• Debounced aria-live="polite" announcement (600ms, via a visually-hidden .input-char-counter__announcer) so screen readers aren't overwhelmed on every keystroke
• Forwards the maxLength to the underlying <input> element for native browser enforcement
• Warning styling (danger color + bold text) when within 10% of the limit

src/components/CreateStreamModal.css

• Added .input-char-counter, .input-char-counter__text, .input-char-counter--warning, and .input-char-counter__announcer styles

src/components/__tests__/InputField.characterCounter.test.tsx

• 8 tests covering: no counter without maxLength, counter display, live update while typing, aria-describedby linkage, warning threshold, debounced announcement, and maxlength attribute forwarding

Testing

• ✅ 8 new character counter tests pass
• ✅ Existing InputField tests unaffected (2 pre-existing failures unrelated to this change — Property 11 has an undefined input variable, and the debounced validation test has a timer interaction issue)
• ✅ WCAG 2.1 AA compliant (counter linked via aria-describedby, debounced aria-live="polite", warning not color-only — also bolds the text)