feat: add support top contact speed split

[mwz-iot]

Description

This PR adds support top contact speed control for normal supports.

What Changed

A new support top contact speed option is added under Speed settings. When enabled, the top contact/interface area of normal supports can use separate speeds for different contact-layer positions:

• First layer contact speed
• Middle layer contact speed
• Top layer contact speed

When the option is disabled, all affected paths fall back to the existing support_interface_speed, preserving the previous behavior.

Implementation Details

The implementation classifies support top contact paths by their semantic support layer type instead of using Z-distance heuristics.

The previous height-based approach was removed. The new logic uses TopInterface / TopContact layer information and contiguous interface-layer block detection:

• TopContact is treated as the top contact layer.
• The bottommost TopInterface layer in a contact block is treated as the first contact layer.
• Intermediate TopInterface layers are treated as middle contact layers.
• Non-top-interface/contact support layers act as block boundaries.

The new First/Middle/Top extrusion role variants are internal implementation details only. They are used to select the correct speed during G-code generation, but they are not exposed as separate user-visible feature types.

UI / Preview Behavior

The feature is presented as part of Support interface / support top contact speed control.

• Statistics remain grouped under Support interface.
• Feature type legend remains grouped under Support interface.
• First/Middle/Top are not shown as separate feature types or separate legend entries.
• Speed preview still shows the actual resulting speeds, so first/middle/top layers can display different colors in Speed view.
• Hovering paths in Speed view shows the actual generated speed.

Path Coverage

The per-layer speed selection applies to the whole corresponding support top contact layer, including:

• internal support interface paths
• contact/interface perimeter loops
• contact boundary/outer loops

This keeps the outer loop and internal contact pattern consistent within the same contact layer.

Compatibility

When support top contact speed control is disabled:

• Existing support_interface_speed behavior is preserved.
• Cached/internal First/Middle/Top roles are guarded during G-code speed selection and fall back to support_interface_speed.
• Existing projects and profiles without the new settings load with default disabled behavior.

The following paths are intentionally unchanged:

• tree support
• bottom contact/interface
• raft
• generic support base paths

Localization

This PR adds localization entries for the new support top contact speed strings.

It also fills the existing baseline translation gap for Support transition speed.

Screenshots/Recordings/Graphs

Please attach screenshots showing:

1. The new support top contact speed settings in the Speed tab.

2. Speed preview with the option enabled, showing different speeds for first/middle/top contact layers.

3. Feature/statistics view showing these paths still grouped as Support interface.

4. Speed preview with the option disabled, showing fallback to support_interface_speed.

Tests

Manual validation completed:

• support_interface_top_layers=1, option ON:
  • top contact speed is applied correctly.
• support_interface_top_layers=2, option ON:
  • first and top contact speeds are applied correctly.
• support_interface_top_layers=3+, option ON:
  • first, middle, and top contact speeds are applied correctly.
• Option OFF:
  • all affected paths fall back to support_interface_speed.
• Toggling the option ON/OFF and slicing again without changing other support settings refreshes correctly.
• Changing first/middle/top speed values refreshes slicing output correctly.
• Internal contact paths and outer/contact loops use the same per-layer speed.
• Feature legend/statistics do not expose First/Middle/Top as separate feature types.
• Speed preview hover displays the actual generated speed.
• Tree support is unaffected.
• Bottom contact/interface is unaffected.
• Raft behavior is unaffected.

Known behavior:

• TopContact is generated independently from support_interface_top_layers.
• support_interface_top_layers controls TopInterface layers, not the total visible top contact layer count.
• In overlap/union cases, source contact regions may already be merged by support generation before speed classification.

2. Speed preview with the option enabled, showing different speeds for first/middle/top contact layers.
3. Feature/statistics view showing these paths still grouped as Support interface.
4. Speed preview with the option disabled, showing fallback to support_interface_speed.

[github-actions]

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