Add Designer/runtime layout parity test suite

[ProGraMajster]

Summary

Adds a deterministic, headless Designer/runtime layout parity harness. It builds equivalent trees and compares actual DesignerLayoutEngine geometry with real ModernFormsNext controls laid out through the production runtime Control.PerformLayout path. The harness records normalized structured snapshots and emits scenario, control path, property, runtime value, and Designer value for every mismatch; it does not contain a second Dock/Anchor/Padding algorithm.

Coverage

• Dock, Anchor, Padding, Margin, MinimumSize/MaximumSize, and visibility
• nested containers, clipping, child order, and repeated resize
• Form and UserControl roots, including nested UserControls
• live Property Grid edits
• .mfdesign save/reopen serialization
• generated Designer code compilation and runtime execution
• reverse parser reconstruction
• final-geometry hit testing
• logical-to-device edge parity at 100%, 125%, 150%, and 200%

Bugs found and fixed

• hidden Designer children incorrectly participated in Dock layout and hit testing
• Designer min/max constraints were not reflected in effective layout bounds
• Designer Fill incorrectly consumed the remaining docking rectangle
• root resize could persist Anchor drift instead of the final runtime-equivalent geometry
• basic Flow layout ignored Margin and default Table auto strips did not match runtime behavior
• generated Form roots assigned outer Size instead of semantic ClientSize
• reverse parsing did not accept composite bitwise enum flags
• ScrollableControl could reinitialize Anchor data during a bounds-driven resize before runtime layout consumed it

Regression coverage

• Designer does not visually apply container Padding during layout #31 asymmetric Padding parity
• UserControl root resize and nested UserControls
• Dock + Padding
• Anchor resize and return-to-original-size drift
• safe custom UserControl atomic preview boundaries remain covered by existing Designer tests

Validation

• parity suite: 78/78 passed, 0 skipped
• Designer tests: 275/275 passed, 0 skipped
• all tests: 1218/1218 passed
• full Debug build: passed, 0 warnings / 0 errors
• full Release build: passed, 0 warnings / 0 errors
• VSIX Debug and Release validation: passed, 0 warnings / 0 errors
• release documentation tests: 32/32 assertions passed
• git diff --check: clean

The parity suite is deterministic and headless: no flaky retry mechanism, no Thread.Sleep, no monitor-derived DPI dependency, and no visible-window requirement.

Follow-ups

• advanced Flow/Table/AutoSize/spans/right-to-left coverage: Complete right-to-left FlowLayout and TableLayout behavior #89
• inherited Form/UserControl roots: Add inherited Form and UserControl Designer support #39
• Designer undo/redo transactions around live edits: Add Designer undo/redo and transaction system #33
• reusable public TestHost primitives and optional rendered/pixel snapshots: Add headless TestHost and application UI testing infrastructure #64
• oversized-Padding negative runtime rectangles remain an explicitly documented representation boundary for nonnegative Designer bounds

Closes #42