Fix native toolbar overlap and task canvas seams

[StephenHsu-filwy]

Summary / 摘要

• remove the task-header and home-composer slogans that are absolutely positioned over native controls
• replace the wide-task hard 64% split with one continuous 240–320px reading veil over the existing body artwork
• keep the composer as one complete surface by clearing clipping/masks and restoring its one-pixel boundary in wide artwork mode
• bump the six release version sources consistently to 1.5.6

GitHub baseline audit / 远端基准审计

This revision was rebuilt from upstream GitHub main at
3aaaf7d6829b376d65f2e19d62ae1f67262c2c02, not from the mixed local
working tree.

• main is three documentation-only commits ahead of public v1.5.5
  (c020d2461225e965f1f3c426959773b26d23799d).
• The relevant runtime blobs on main are byte-identical to v1.5.5.
• Upstream CSS still contains the two absolutely positioned header labels,
  the floating home quote, the wide composer border: 0, the hard 64%
  task gradient, and the task shell overflow: hidden.
• The original broad patch was explicitly reverted. The final PR no longer
  changes documented safeArea behavior, alerts/toasts, global focus or
  disabled states, sidebar structure, selectors, or injector readiness logic.
• Net diff against current main: 16 files, 221 additions, 251 deletions.

Type / 类型

• Bug fix / 缺陷修复
• Feature / 新功能
• Docs / 文档
• Theme / CSS / visual / 主题或视觉
• Scripts / install / restore / 脚本或安装恢复
• Chore / 杂项

Platform / 平台

• macOS
• Windows
• Both / 双平台
• Docs / repo only / 仅文档或仓库元数据

Self-check / 自测

macOS

• macos/tests/run-tests.sh passed
• Doctor (requires an installed signed runtime)
• Live verify (requires an installed signed runtime)
• Restore / re-apply smoke (install/restore/start paths are unchanged)

Windows

• node --test windows/tests/*.test.mjs passed (11/11)
• PowerShell and Setup.exe tests (pending GitHub Windows CI)
• Environment noted below

User-facing / 用户可见变更

• Updated macos/CHANGELOG.md and all six release version sources
• N/A — no user-facing change

Security / 安全

• Does not modify official Codex install / asar / signatures
• Does not silently write API Base URL or keys
• CDP remains loopback-oriented (127.0.0.1)

Notes / 补充

• Shared runtime sync check, selector doctor, renderer runtime tests, syntax checks and both platform payload checks passed.
• macOS repository suite passed using the installed compatible macOS 15.4 SDK. Tests that require an installed signed app session were skipped through their documented switches.
• A local universal arm64/x86_64 CodexDreamSkin-v1.5.6.dmg was built, ad-hoc signed, mounted and validated successfully.
• Windows PowerShell 5.1/7 and Inno Setup validation remain mandatory in repository CI.