feat: bandar and broker totals for one investor side

IPOT's investor filter splits each broker row by client domicile, but its
footer then gives only that side's buying (BBCA 2026-10-16: foreign 1.7 T,
domestic 4.9 T of 6.6 T). The foreign net gives the selling on all boards:
foreign 1.7 + 2.3 = 4.0 T (IDX: about 3.95 T regular), domestic
4.9 - 2.3 = 2.6 T.

- BrokerSummary gains buy_value and sell_value: the total for all
  investors, the footer and the derived selling for one side (selling is
  null with a board filter, where the net covers other boards).
- Bandar weighs the top N buyers' share of the value bought against the
  top N sellers' share of the value sold, so `--investor foreign|domestic`
  reads that side alone; for all investors the readings are unchanged.
  One side on one board is refused, as there is no selling to weigh.
- Tables print what the side bought and sold; fixtures for foreign and
  domestic on all boards were recorded from IPOT.

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

@@ -31,14 +31,15 @@ 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 {
+/// One investor side is weighed against its own selling, which the source
+/// gives only across all boards.
+fn check_scope(investor: BrokerInvestor, board: BrokerBoard) -> Result<(), IdxError> {
+    if investor == BrokerInvestor::All || board == BrokerBoard::All {
         Ok(())
     } else {
         Err(IdxError::InvalidInput(format!(
-            "bandar needs --investor all: the broker summary has no total for {} investors alone",
+            "bandar for {} investors needs --board all: the broker summary gives one side's \
+selling only across all boards",
             investor.as_str()
         )))
     }
@@ -70,7 +71,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<Fetched<BandarReport>, IdxError> {
         let top = check_top(query.top)?;
-        check_investor(query.investor)?;
+        check_scope(query.investor, query.board)?;
         let summary =
             self.idx
                 .broker()
@@ -87,7 +88,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<BandarScreen, IdxError> {
         check_top(query.top)?;
-        check_investor(query.investor)?;
+        check_scope(query.investor, query.board)?;
         let mut reports = Vec::new();
         let mut failures = Vec::new();
         for symbol in symbols {