Editor: right-to-left lines align right and move by what is on screen (#134)

[fadyehabamer]

Fixes #134.

Right-to-left lines now align right, and the arrow keys and Vim h/l move the way they point on screen.

How

• Per-line direction. Each line takes the direction of its first strong letter. Leading Markdown syntax is skipped first: list markers, task boxes, heading hashes and quote markers. Otherwise the x of - [x] مهمة would make an Arabic task line left-to-right, which is what dir="auto" would do. Marks and digits are not strong, so 123 שלום is right-to-left. An explicit LRM/RLM/ALM decides when present.
• Rendering and arrow keys. Right-to-left lines get dir="rtl" through a line decoration, which only covers visible lines. EditorView.perLineTextDirection is enabled, so CodeMirror reads each line's direction: the line aligns right because text-align is start, and the default arrow-key commands, which are already visual and bidi-aware, move the right way.
• Vim. h/l move by the same per-line direction, like Vim's rightleft, in normal, visual and operator-pending mode. <Left>/<Right> are mapped too, because Vim forwards them to its built-in h/l without remapping. x, <BS> and <Space> stay logical. Registered next to registerDisplayLineMotion in each window that sets up Vim: the main editor, quick capture, the floating note and external files.

The new code is in lib/cm-bidi.ts, and bidiExtension is added next to markdownListIndentPlugin in every editor surface.

Tests

lib/cm-bidi.test.ts, 25 tests:

• direction detection, including Markdown prefixes, mixed lines, digits and marks
• the rendered dir attributes, and that they follow edits
• h/l, counts, <Left>/<Right> and dl in left-to-right and right-to-left lines

npm run test:run in app-core: 2879 passed. tsc --noEmit is clean.

Known limits

• In a line that mixes directions, Vim h/l follow the line's direction, as the issue suggests. Insert-mode arrow keys use CodeMirror's own visual movement, which handles mixed text fully.
• Nested list indentation and the list guides still sit on the left in a right-to-left list. They come from padding-left and the guide backgrounds in cm-markdown-list-indent, so I'd keep that as a follow-up.

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