Closes the last #946 gap (СМР). Fetches «Индексы цен производителей на
строительную продукцию по РФ» from the OPEN Rosstat xlsx
(rosstat.gov.ru/storage/mediabank/Invest_ind_stroitel_MM-YYYY.xlsx),
parses the monthly «к предыдущему месяцу» section → macro_indicator
(indicator_type='construction_price_index', region='rf', monthly, %).
The reCAPTCHA-gated fedstat dataGrid.do path is DELIBERATELY NOT used —
the open Rosstat source needs no captcha. EMISS id=31108 documented as a
prod-only SDMX alternative (not wired).
URL is date-derived with bounded look-back (filename changes monthly;
_fetch_construction_latest walks current month back to 6, first 200 wins;
year-boundary handled, exhaustion raises, 404 breaks fast — no hang).
Wired into rosstat_macro_sync with per-source try/except (can't break
demography/income) + SAVEPOINT-per-row. None-not-0 on blank months.
33 tests (incl look-back + year-boundary + graceful), ruff clean.
Note: no construction-cost channel in macro_coefficient yet (demand-side
only) — series is ingested/available for future cost-side use + display.
Refs #946
