fix(fundamentals): A4a review — stricter null semantics in derivation

1. net_debt requires BOTH cash and total_debt; a missing side is null, not
   treated as zero (which would be a partial, misleading value).
2. net_debt_to_ebitda is null when TTM EBITDA <= 0 — a negative denominator
   would otherwise rank a distressed issuer as favorably low-leverage.
3. The quarter tape is the CONSECUTIVE run ending at the latest period (stops at
   a gap), so trend text never compares non-adjacent quarters as if consecutive.
4. YoY growth is null when the prior-year TTM is <= 0 (e.g. loss->profit), which
   is not a meaningful percentage.

Also corrected the plan's net-debt formula to total debt − (cash + ST) matching
the positive-means-net-debt implementation. +4 tests. 10 passed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/dolt-integration-plan.md

@@ -244,7 +244,7 @@ that scoring already reads, refreshed daily by step (c) after activation.
 | EPS growth YoY | TTM diluted EPS vs prior TTM | snapshot |
 | Operating margin + 4q trend | TTM operating income / revenue | snapshot |
 | FCF margin | (TTM CFO − capex) / revenue | snapshot |
-| Net cash / net debt | cash + ST investments − total debt | snapshot |
+| Net debt | total debt − (cash + ST investments); positive = net debt | snapshot |
 | Net debt / EBITDA | net debt / TTM EBITDA | snapshot |
 | Share count Δ YoY | shares outstanding vs year ago | snapshot |
 | Trailing P/E | price / TTM diluted EPS | request time |