fix: align rectangular task markers with text - #5700

Related issue: none found; reported with screenshots during local validation.

Summary

Rectangular task markers in Ulysses, Graphite, and One Dark sit above the first text line because their top offset uses 0.1em; native inputs retain their browser font size. Center the 16px markers using the editor font-size and line-height variables, and use the logical inline inset consistently.

Apply Graphite and One Dark styles to both input and span markers so both DOM representations render the same square shape and checked state.

Before: checked and unchecked squares sit above the text center. After: both align with the first line as editor typography changes.

Type of change

• Bug fix (non-breaking, fixes an issue)
• New feature (non-breaking, adds functionality)
• Breaking change (causes existing functionality to change)
• Documentation update

Test plan

• New tests added: CSS-only positioning change; visual verification required.
• Manually tested on macOS: dev app launched for user validation; final cross-theme validation pending.
• git diff --check passed.
• Prettier reports only existing float-shadow formatting in these files.
• pnpm run lint blocked: ESLint cannot resolve globals.
• pnpm run typecheck blocked: E2E specs cannot resolve playwright, with resulting implicit-any errors.

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.