fix incorrect retargeting by using bridge ref.

[koculu]

Fixes :model / single-prop retargeting regression by introducing stable bridge ref handling in single-prop.

What changed

• Added bridge-based sync for ref props to avoid mutating previously selected source items on retarget.
• Kept nested forwarded bindings working by recognizing forwarded bridge refs.
• Simplified single-prop flow with helper functions and clearer branching.
• Added detailed inline documentation for the algorithm.

Tests

• Expanded tests/directives/model.spec.ts with regressions for:
  • direct + component retargeting
  • number input retargeting
  • multi-replacement and nested 3-level forwarding
  • list-selection regression (previous item should not be overwritten)