fix(tui): fix Linux Ctrl+C regression, remove double clipboard write

- Fix critical regression: on Linux, Ctrl+C could not interrupt/clear/exit
  because isAction(key,'c') shadowed the isCtrl block (both resolve to k.ctrl
  on non-macOS). Restructured: isAction block now falls through to interrupt
  logic on non-macOS when no selection exists.
- Remove double pbcopy: ink's copySelection() already calls setClipboard()
  which handles pbcopy+tmux+OSC52. The extra writeClipboardText call in
  useInputHandlers copySelection() was firing pbcopy a second time.
- Remove allowClipboardHotkeys prop from TextInput — every caller passed
  isMac, and TextInput already imports isMac. Eliminated prop-drilling
  through appLayout, maskedPrompt, and prompts.
- Remove dead code: the isCtrl copy paths (lines 277-288) were unreachable
  on any platform after the isAction block changes.
- Simplify textInput Cmd+C: use writeClipboardText directly without the
  redundant OSC52 fallback (this path is macOS-only where pbcopy works).

ui-tui/src/components/appLayout.tsx

@@ -6,7 +6,6 @@ import type { AppLayoutProgressProps, AppLayoutProps } from '../app/interfaces.j
 import { $isBlocked } from '../app/overlayStore.js'
 import { $uiState } from '../app/uiStore.js'
 import { PLACEHOLDER } from '../content/placeholders.js'
-import { isMac } from '../lib/platform.js'
 import type { Theme } from '../theme.js'
 import type { DetailsMode } from '../types.js'
 
@@ -236,7 +235,6 @@ const ComposerPane = memo(function ComposerPane({
             <Box flexGrow={1} position="relative">
               <TextInput
                 columns={Math.max(20, composer.cols - pw)}
-                allowClipboardHotkeys={isMac}
                 onChange={composer.updateInput}
                 onPaste={composer.handleTextPaste}
                 onSubmit={composer.submit}