refactor(tui): tighten editor handoff helpers

- editor.ts: collapse two private helpers into one flatMap-driven lookup,
  keep `isExecutable` as the only named primitive, document the fallback
  chain with prompt_toolkit parity
- editor.test.ts: hoist the `exe` helper out of `describe`, drop the
  empty afterEach + dead mkdir branch, materialize expected paths before
  the resolveEditor call so argument evaluation order doesn't bite
- useComposerState.openEditor: rmSync the mkdtemp dir (was leaking),
  early-return on bad exit / empty buffer, run cleanup in finally
- useInputHandlers: cheap `ch.toLowerCase() === 'g'` guard before the
  modifier check
- hermes-ink/screen.ts: pick up `npm run fix` import-sort cleanup so
  lint passes

ui-tui/packages/hermes-ink/src/ink/screen.ts

@@ -1,6 +1,6 @@
-import { ansiCodesToString, diffAnsiCodes, type AnsiCode } from '@alcalzone/ansi-tokenize'
+import { type AnsiCode, ansiCodesToString, diffAnsiCodes } from '@alcalzone/ansi-tokenize'
 
-import { unionRect, type Point, type Rectangle, type Size } from './layout/geometry.js'
+import { type Point, type Rectangle, type Size, unionRect } from './layout/geometry.js'
 import { BEL, ESC, SEP } from './termio/ansi.js'
 import * as warn from './warn.js'