[Task] Fix result metadata and shadow-price rendering from MUIO v5.5

[SeaCelo]

This one still needs to stay a bundle.

The important change here is not for MUIOGO to make local decisions about upstream result semantics. The important change is for MUIOGO to correctly honor upstream v5.5 result metadata and variable definitions.

That means the default rule here is:

• upstream Variables.json is the source of truth
• MUIOGO should adapt its result rendering, registry, unit generation, and Pivot behavior so upstream metadata works correctly

What should land here:

• adopt upstream Variables.json as-is
• expose the upstream-owned result groups and metadata correctly in the MUIOGO frontend
• make MUIOGO's result handling honor upstream unit rules and grouping cleanly
• keep existing result screens working while aligning them to upstream v5.5 metadata

What should not land here:

• no local reinterpretation of upstream units or semantics by default
• no formatting-only churn in Parameters.json
• no splitting this into half-ported frontend changes that leave result screens inconsistent

Parameters.json stays out of scope unless we find a semantic upstream change that actually matters. Current evidence still points to formatting-only churn there.

Done when:

• upstream v5.5 result metadata is loaded as-is
• MUIOGO renders those result groups and units correctly
• Pivot works on the demo data with the upstream metadata
• existing non-broken result screens do not regress

Related work:

• [Task] Absorb selected MUIO v5.5 changes on origin/main #388 [Task] Absorb selected MUIO v5.5 changes on origin/main (OPEN)
• [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390 [Task] Pull the safe backend/runtime changes from MUIO v5.5 (OPEN)
• [Task] [Proposal/Architecture] Canonical CLEWS Result Extraction & Validation Layer for OG-Core Integration #348 [Task] [Proposal/Architecture] Canonical CLEWS Result Extraction & Validation Layer for OG-Core Integration (OPEN)
• Feature: Unified User Interface for OG-Core and OSeMOSYS Integration (OG-CLEWS Framework) #380 Feature: Unified User Interface for OG-Core and OSeMOSYS Integration (OG-CLEWS Framework) (OPEN)