fix(core): symmetric bandar thresholds; bandar needs all investors

- Basis points truncate toward zero instead of flooring, so a reading of
  -4.9952% stays neutral like its mirror image and -14.9952% stays
  distribution; tests cover both signs at both thresholds through
  bandar_tier. Goldens move by the rounding (BBCA top 5: -2426 -> -2425).
- With one investor side selected the summary has no total to weigh
  brokers against, so bandar and analyze_bandar reject it (INVALIDINPUT)
  instead of reading every tier as missing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3syn2fN2LNo5pvTSqc6eh

crates/idx-core/src/analysis/mod.rs

@@ -31,6 +31,19 @@ pub struct Comparison {
     pub failures: Vec<(String, IdxError)>,
 }
 
+/// Readings weigh brokers against the value traded, which the source does
+/// not total for one investor side.
+fn check_investor(investor: BrokerInvestor) -> Result<(), IdxError> {
+    if investor == BrokerInvestor::All {
+        Ok(())
+    } else {
+        Err(IdxError::InvalidInput(format!(
+            "bandar needs --investor all: the broker summary has no total for {} investors alone",
+            investor.as_str()
+        )))
+    }
+}
+
 /// Bandar readings for several symbols, strongest accumulation first;
 /// symbols that failed are listed with their error.
 pub struct BandarScreen {
@@ -57,6 +70,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<Fetched<BandarReport>, IdxError> {
         let top = check_top(query.top)?;
+        check_investor(query.investor)?;
         let summary =
             self.idx
                 .broker()
@@ -73,6 +87,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<BandarScreen, IdxError> {
         check_top(query.top)?;
+        check_investor(query.investor)?;
         let mut reports = Vec::new();
         let mut failures = Vec::new();
         for symbol in symbols {