feat: per-BU trend lines in counts history chart

- Create ivanti_counts_history_by_bu table (bu_ownership, state, count per sync)
- Sync writes per-BU snapshot alongside global history on each sync
- Seed table with current counts for immediate first data point
- GET /counts/history accepts ?teams param — queries per-BU table when filtered
- IvantiCountsChart accepts teamsParam prop, re-fetches on scope change
- ReportingPage passes getActiveTeamsParam() to the chart
- Historical per-BU data accumulates from this point forward
- Global history (no filter) still uses the original aggregate table

backend/db-schema.sql

@@ -248,6 +248,17 @@ CREATE TABLE IF NOT EXISTS ivanti_counts_history (
     recorded_at TIMESTAMPTZ DEFAULT NOW()
 );
 
+CREATE TABLE IF NOT EXISTS ivanti_counts_history_by_bu (
+    id SERIAL PRIMARY KEY,
+    bu_ownership TEXT NOT NULL,
+    state TEXT NOT NULL CHECK (state IN ('open', 'closed')),
+    count INTEGER NOT NULL DEFAULT 0,
+    recorded_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_counts_history_bu ON ivanti_counts_history_by_bu(bu_ownership);
+CREATE INDEX IF NOT EXISTS idx_counts_history_bu_date ON ivanti_counts_history_by_bu(recorded_at);
+
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 -- Ivanti FP (False Positive) submissions
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