fix: horizontal scroll, Home/End keys, and line operations in SQL editor

[datlechin]

Summary

• Fix horizontal scrolling for long lines (upstream bug in CodeEditTextView)
• Add Home/End key support with all modifier combinations (bug: Home and End keys don't work in the SQL editor #448)
• Add duplicate line (Cmd+Shift+D), delete line (Cmd+Shift+K), move line up/down (Option+Up/Down)
• Fix move line up/down for last-line and emoji content edge cases

Root Causes

Horizontal scroll: Variable shadowing bug in CodeEditTextView layoutLine() — var maxFoundLineWidth = maxFoundLineWidth shadowed the inout param, so maxLineWidth never updated. Also patched styleTextView() to respect wrapLines.

Home/End: AppKit maps Home/End to scrollToBeginningOfDocument:/scrollToEndOfDocument: which only scroll without moving cursor. CodeEditTextView didn't override these.

Line operations: moveLinesUp()/moveLinesDown() existed but were never wired to key bindings. Also had bugs with trailing-newline handling and UTF-16 string splitting.

Changes

• CodeEditTextView (vendored): fix maxFoundLineWidth shadowing, add Home/End handling in keyDown, add moveToBeginningOfLine/moveToEndOfLine/centerSelectionInVisibleArea overrides
• CodeEditSourceEditor: patch styleTextView()/styleScrollView() for horizontal scroll, wire Cmd+Shift+D/K and Option+Up/Down in handleCommand, add duplicateLine()/deleteLine(), rewrite moveLinesUp()/moveLinesDown() with correct newline and UTF-16 handling
• SQLEditorCoordinator: remove fragile horizontal scroll workaround, fix redundant double dispatch in settings observer

Test plan

• Type long line with word wrap off — horizontal scroll works
• Home/End moves to start/end of line
• Cmd+Home/End moves to start/end of document
• Shift variants extend selection
• Cmd+Shift+D duplicates current line
• Cmd+Shift+K deletes current line
• Option+Up/Down moves line up/down
• Move line works correctly on last line (no trailing newline)
• Undo works after all line operations