feat(editor): select line on CodeMirror line number gutter click

[bajrangCoder]

No description provided.

[greptile-apps]

Greptile Summary

This PR adds line-number gutter click selection to the CodeMirror editor, wiring a new handleLineNumberClick helper into makeLineNumberExtension for both standard and relative line-number modes. Plain clicks select the full line with the cursor anchored at the line start; shift-clicks extend the current selection by whole lines. Previous review concerns (falsy || from fallback, missing shift-click support, cursor landing at the next line) are all addressed in the new implementation.

Confidence Score: 5/5

Safe to merge; all remaining findings are P2 style/UX suggestions that do not block correct behavior.

All P0/P1 concerns from prior rounds are resolved. The two open items are a minor cursor-position UX inconsistency in the downward shift-extend path and a trivial redundant wrapper — neither causes incorrect data or a broken user path.

src/cm/lineNumberSelection.ts — createExtendedLineSelection downward-direction cursor placement.

Important Files Changed

Filename	Overview
src/cm/lineNumberSelection.ts	New module implementing line-number gutter click selection; null-safety and cursor placement are well-handled for the plain-click path, but the downward shift-extend direction leaves the cursor one position past the trailing newline (next-line column 0).
src/lib/editorManager.js	Imports and wires handleLineNumberClick into both the standard and relative-line-number configurations via lineNumberConfig.domEventHandlers; the wrapper arrow function is redundant but harmless.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Gutter click event] --> B{button === 0?}
    B -- No --> Z[ignore]
    B -- Yes --> C{alt / ctrl / meta?}
    C -- Yes --> Z
    C -- No --> D[getLineSelectionRange]
    D --> E{range resolved?}
    E -- No --> Z
    E -- Yes --> F{shiftKey?}
    F -- No --> G[createLineSelection\nanchor=to, head=from\ncursor at line start]
    F -- Yes --> H[createExtendedLineSelection\nmerge current + clicked range]
    H --> I{clicked above\ncurrent?}
    I -- Yes --> J[single to, from\ncursor at start]
    I -- No --> K[single from, to\ncursor past newline ⚠️]
    G --> L[view.dispatch + view.focus]
    J --> L
    K --> L

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_{Reviews (2): Last reviewed commit: "fix" | Re-trigger Greptile}

[bajrangCoder]

@greptileai