fix(demo): use bare tag ids for gauge variableId bindings

[sankalpsthakur]

Summary

Demo project used legacy Device^~^Tag variableId form that never matches runtime bare tag ids. Corrected demo bindings to bare tag ids.

Changes

• Updated all 13 variableId values in client/src/assets/project.demo.fuxap:
  • Device A^~^Tag Byte → Tag Byte (4 bindings)
  • Device A^~^Tag Bool → Tag Bool (9 bindings)
• Left variable / variableSrc and HmiService.toVariableId() unchanged (demo-only, high merge odds).

Validation

• inspected demo JSON / grep for remaining ^~^ in demo project (0 remaining)
• parsed demo project as JSON; all 13 variableId values are bare declared tag ids (Tag Byte, Tag Bool) matching devices["Device A"].tags

Fixes #2486

AI/LLM disclosure

• AI coding tools (including Grok and/or Codex agent-assisted editing) were used to help draft or modify code and this PR description.
• I reviewed the complete change, understand the reasoning, and ran the reported local tests before submitting.
• This submission is original work of authorship under the project contributor terms; AI output was not pasted unreviewed.