fix(USMetrics): anchor trend windows to the latest observation; report rate series in percentage points - #2253

Problem

calculateTrend() in LifeOS/install/skills/USMetrics/Tools/GenerateAnalysis.ts anchored every trend window to today and took the first observation after the cutoff as the start. Monthly and quarterly FRED series lag the calendar by 1–3 months, so the "1Y" column silently covered a shorter span, and FRED's missing-value observations (.) pushed the start further forward.

Reproduced on 2026-09-27 against live FRED data (before this change):

A second defect in the same column: percent change applied to series that are already percentages produced lines such as GDP Growth Rate: +200.0% and Fed Funds Rate: +807% over 10 years.

Fix

• Anchor each window to the latest observation; choose the start as the observation nearest to latest − N years.
• Return null (rendered —) when no observation lies within tolerance of the target, instead of a mislabelled window. Tolerance is half the series' median observation spacing, floored at 3 days (covers weekends/holidays in daily series).
• Fetch years + 1 of history so the 10Y window has a real start candidate for lagged series.
• Sort observations by date before windowing.
• Series in RATE_SERIES (UNRATE, FEDFUNDS, DGS10, …) report changes in percentage points; formatValue now reuses the same set (GDP Growth Rate previously printed as a bare number). One SCALE table holds the dead band / "significant move" / momentum thresholds per unit, used by the snapshot, detail tables, extremes and momentum sections.
• Export the pure functions and guard main() with import.meta.main so the module is testable; add GenerateAnalysis.test.ts (fixed-date fixtures, no wall-clock dependence).

Verification

• bun test LifeOS/install/skills/USMetrics/Tools/GenerateAnalysis.test.ts: 14 pass, 0 fail.
• Live run after the change (2026-09-27): CPI +3.4%, Real GDP +2.1%, Core PCE +3.3%, U-3 −0.20pp, GDP Growth Rate −2.30pp, Fed Funds −0.70pp, 10Y +1.02pp, 30Y mortgage +0.73pp, all equal to values computed directly from date-matched FRED observations.
• Independent re-derivation from FRED (separate script, same day) matched all 12 snapshot series; simulating the old method against the same data reproduced wrong values on 10 of 12 (e.g. UMCSENT −3.5% vs true −11.2%, PSAVERT −0.90pp vs true −1.50pp).
• No — cells appear in the live detail tables (every priority series has a start within tolerance for all four horizons).

Not in this PR (follow-ups)

• Tools/FetchFredSeries.ts has its own calculateTrendStats with the same anchored-to-today logic; a shared trend module would let both tools use one implementation.
• RATE_SERIES, SERIES_NAMES and FetchFredSeries.ts's CORE_SERIES are three hand-maintained series tables; consolidating them is a larger change.

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