feat(forecasting): §13 SiteFinderReport structural object (#987, 955-A1)
Add frozen, JSON-serializable SiteFinderReport container with 8 nested section
dataclasses (exec_summary, market_now, future_market, product_tz, scenarios,
scoring, confidence, meta). Pure container — no DB/compute/LLM; populated by
#988 assembler, consumed by #989 exporters + #957 chat. All fields
optional/defaulted (partial report valid); as_dict() JSON-safe (dates→iso);
advisory=True; schema_version "1.0". 14 unit tests.
Light1YT
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