Adds StdinBuffer class (adapted from OpenTUI, MIT license) to split
batched stdin into individual sequences before they reach components.
This fixes key presses being dropped when batched with release events,
which commonly occurs over SSH due to network buffering.
- Each handleInput() call now receives a single event
- matchesKey() and isKeyRelease() work correctly without batching awareness
- Properly buffers incomplete escape sequences across chunks
- Handles bracketed paste mode
Addresses #538
