fix(sec): correct fundamentals derivation from SEC company facts

The A5 parity report surfaced coverage gaps and wrong values that all traced
to the SEC facts parser and read-time derivation rather than to bad source
data. Fixes, each validated by replaying the production parser + derivation
against live company facts:

- Period identity is derived from period_end against the issuer's fiscal
  calendar, not SEC's fy/fp fields, which collide (two period ends on one key,
  one silently discarded) and invert (a period sorting before one that precedes
  it) often enough to break the quarter chain. Recovers BXP, CRM, CRWD, FRT,
  MTD, NTAP, PPL, STX, WDAY. Fixed labels are internal ordering keys only (not
  in any API schema), so a filer whose year ends in early January shifting by
  one is harmless.
- Revenue concept list gains RevenuesNetOfInterestExpense (banks) and the
  IncludingAssessedTax variant (REITs/consumer); EPS gains the continuing-ops
  variant (REG/FCX) and, last, basic EPS for a period tagging no diluted
  variant at all (PPL). All appended, so any issuer that already resolved keeps
  its concept.
- YTD span tolerance 20 -> 25 days, covering 4-4-5 retail calendars whose
  36-week YTD-Q3 (251-252d) previously missed by ~2 (COST, PEP, DPZ).
- Amendment resolution is per field: a partial 10-K/A (Part III only, no
  financial facts) no longer blanks the period (DVN).
- TTM diluted EPS is suppressed when a split contaminates the trailing window
  (BKNG's mixed-unit sum produced a P/E of 1.10 that clamped to a perfect
  fundamental sub-score). A post-filing split with no share-count evidence
  (KLAC) remains undetectable from this data.
- Multi-class share fallback: weighted_avg_diluted_shares is captured and used
  for market cap when the cover-page count is absent (dimensional, so missing
  from company facts for META/CMCSA/CHTR/FOXA/NWSA/LEN). Within ~0.6% of the
  true count on controls; flagged shares_estimated in the API. BRK-B has no
  weighted-average fact either and stays unavailable.

820 unit tests pass; new tests confirmed to fail against the pre-fix code.
Effect is inert until existing rows are reparsed (see reparse path).

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

app/services/fundamentals_api_service.py

@@ -155,6 +155,13 @@ def _build_valuation(derived, subject_price, peer_derived, peer_price_by_cik, tw
         "pe": _round(pe, 2),
         "fcf_yield": _round(fcf_yield, 2),
         "market_cap_est": _round(market_cap, 0),
+        # market_cap_est and fcf_yield both rest on the share count. When it came
+        # from the weighted-average diluted fallback (multi-class issuers, whose
+        # per-class cover-page count is absent from companyfacts), say so rather
+        # than presenting a period average as a point-in-time count.
+        "shares_estimated": bool(
+            market_cap is not None and derived.shares_outstanding_estimated
+        ),
         "pe_industry": pe_industry,
         "fcf_yield_industry": fcf_yield_industry,
         "price_date": _iso(price_date),