Add backward-compatible JSON upload and release ver.1.4.0

[iguchi-lab]

Summary

• restore JSON upload execution in the Gradio UI
• accept both pre-Next and current *_input.json files
• preserve uploaded values and unknown legacy keys while filling only missing entries with current defaults for the selected heating/cooling model
• validate missing, malformed, non-object, non-UTF-8, and oversized JSON before starting the engine
• release the backward-compatible feature as Verification Platform Next ver.1.4.0

Compatibility

• default_v1.3.0_input.json: loaded without supplementation
• legacy RAC input: 33 newly introduced fields supplemented with current defaults
• legacy RAC input completed an actual 8760-hour engine smoke run and generated input/manifest artifacts
• uploaded JSON does not rewrite the visible form; the effective merged input is shown in the calculation-input tab
• external climate/load files referenced by name are not embedded in JSON and must be available separately

Verification

• pytest -q: 372 passed
• Phase 5: default duct-central and RAC whole-house passed
• engine internal tests: 559 passed, 44 existing numerical-edge RuntimeWarnings, no failures/skips/xfails
• ruff check .: passed