Populate snapshot graph nodes with resolved parameter values

[jitu5]

Parent issue: #2265
Depends on: #2655, #2656, #2657, #2658, #2715

Update: The foundation already provides _InspectionSession.parameters() and a cached config loader that applies runtime parameter overrides. This ticket reuses it; it does not add another loader or manually merge --params values.

Summary

Pass the resolved parameter mapping into GraphBuilder and populate each task node's parameters field in the same shape as the legacy backend.

Scope

• Let GraphBuilder receive resolved parameter values.
• For an input named parameters, attach the complete parameter mapping.
• For params:x, attach {x: value}.
• Resolve dotted names such as params:model_options.test_size from nested configuration.
• Preserve value types and handle a missing value without failing graph construction.
• Add focused parity and edge-case tests.

Runtime provider installation belongs to #2659. Parameter-node /api/nodes/{id} metadata belongs to #2660.

Acceptance criteria

• Task-node parameter mappings match the captured baseline for every demo pipeline.
• Root parameters, individual params:x, dotted keys, and missing keys are covered.
• Resolved values passed to GraphBuilder, including typed runtime overrides returned by _InspectionSession.parameters(), appear in task-node parameter mappings.
• Supplying runtime parameters does not change any node or edge ID.