Add line style selection dropdown to tools panel for drawing new lines

[Copilot]

Previously, users could only draw new lines using the single-color style, which was hardcoded in the line creation logic. This PR adds the ability to select from all available line styles when drawing new lines.

Changes Made

UI Enhancement:

• Added a "Line style" dropdown in the tools panel above the line path buttons
• Dropdown shows localized line style names using the existing localization system
• Only appears when the tools panel is expanded to maintain clean UI

State Management:

• Added selectedLineStyle field to RuntimeState with default value LineStyleType.SingleColor
• Added setSelectedLineStyle action to update the selected line style
• Selected line style persists until user changes it

Line Creation Logic:

• Modified svg-canvas-graph.tsx to use the selected line style instead of hardcoded SingleColor
• Special handling for SingleColor to preserve existing theme functionality
• Other line styles use their proper default attributes

Line Style Component Updates:

• Updated multiple line style components to handle the newLine prop correctly
• When newLine is true, components set pointer-events: none so elementsFromPoint returns the underlying station instead of the line during creation
• Updated components: single-color, dual-color, river, shmetro-virtual-int, china-railway, bjsubway-single-color, bjsubway-dotted

Internationalization:

• Added translations for "Line style" in English, Chinese Simplified, and Chinese Traditional

Usage

1. Expand the tools panel
2. Select desired line style from the "Line style" dropdown
3. Choose a line path type (diagonal, perpendicular, etc.)
4. Draw lines as usual - they will now use the selected line style

The selected line style remains active until changed, allowing users to draw multiple lines with the same style efficiently.

Fixes #1141.

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