[leoafarias]

Removes dead prerelease API. Each item was re-grepped across lib, test, example, tool, website, and skills; nothing real still calls it.

Removed:

• Color.withOpacity, plus the stale ColorPalette sentence
• Listenable.merge and _MergingListenable, and that test group
• TextRange.textBefore, textAfter, and isNormalized, and their tests
• TextEditingValue.composing and its tests
• CursorController.updatePosition (the low-level barrel still exports CursorController)
• PersistentUtf8Text, its unit test, and the snippet lock in native_lifecycle_test.dart
• TERMINAL_TUI_DEBUG_LOG and the dart:io import that only served it
• FocusAttachment.isScope and the unread element getter
• the unused noir_ffi.dart import in bin/health_check.dart

Kept Color.lerp, the *Transparent constants, TextRange.textInside and isValid, and FocusAttachment.isAttached. The PersistentUtf8Text denylist strings in public_api_test and source_package_consumer_test stay.

14 insertions, 330 deletions.

Proof, Dart 3.10.0, from packages/noir:

• dart format --output=none --set-exit-if-changed lib/ test/ example/ bin/ hook/ tool/
• dart analyze --fatal-infos
• dart test --concurrency=1 — 2389 passed. Eight failures and one skip were the uninitialized external/opentui submodule (missing fixtures and git rev-parse walking up to this repo). After git submodule update --init, those tests pass.