feat(editor): add configurable horizontal scroll margin to CodeMirror

[bajrangCoder]

Summary

• add horizontal scroll-past-end space for CodeMirror when word wrap is disabled
• restore the existing editor margin behavior previously available with Ace
• expose the margin under Editor settings → Scroll settings
• update the horizontal scrollbar to use CodeMirror’s actual padded scroll width
• add localized labels and unit coverage

Closes: #2398 #2277

[greptile-apps]

Greptile Summary

Adds a configurable horizontal scroll margin for unwrapped CodeMirror editors.

• Applies the configured margin as right-side content padding and reconfigures open editor panes when the setting changes.
• Exposes a validated whole-pixel input under scroll settings.
• Updates scrollbar width calculation to use CodeMirror’s padded scroll width.
• Adds language keys and unit coverage for margin normalization and theme generation.

Confidence Score: 4/5

The PR appears safe to merge, with the non-blocking caveat that the new setting remains untranslated in every non-English locale.

The editor setting, compartment reconfiguration, and scrollbar integration are coherently wired; the only accepted issue is duplicated English UI copy in localized language bundles.

Files Needing Attention: src/lang/*.json

Important Files Changed

Filename	Overview
src/cm/scrollPastEnd.ts	Adds a bounded horizontal-margin theme for unwrapped CodeMirror content.
src/lib/editorManager.js	Integrates the horizontal margin with the wrap compartment, live setting updates, and native scroll-width measurement.
src/settings/scrollSettings.js	Adds a non-negative whole-pixel margin input and stores its value numerically.
tests/unit/scrollPastEnd.test.js	Covers theme generation, zero and invalid input handling, and fractional-value rounding.
src/lang/ar-ye.json	Adds the required keys but leaves their values in English, as do the other changed non-English locale bundles.
bun.lock	Records the Vitest dependency graph used by the new unit test setup.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    Settings[Scroll settings: leftMargin] --> Store[appSettings.update]
    Store --> Event[update:leftMargin]
    Event --> Options[applyOptions textWrap]
    Options --> Wrap{Word wrap enabled?}
    Wrap -->|Yes| LineWrap[EditorView.lineWrapping]
    Wrap -->|No| Margin[horizontalScrollPastEnd]
    Margin --> Padding[Right padding on cm-content]
    Padding --> Width[scrollDOM.scrollWidth]
    Width --> Scrollbar[Horizontal scrollbar range]

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