feat(core): broker summaries from IPOT

Adds a BrokerSummaryProvider capability served by Indo Premier's public
broker summary page: the top 10 buyers and sellers of a stock by lots over
a date range, with totals. No login or key.

- api/ipot: pure parser (decimal scaling of `1.6 M`-style figures), a
  client that retries the server's spurious 404s, and a fixture mock.
- broker: Broker::summary/latest over the cache (7 days for closed ranges,
  5 minutes for today), range checks, and IDX member names bundled from
  GetBrokerCodeList.
- foreign_net_value is null for filtered summaries: the source does not
  apply the filters to it.

The endpoint's behavior was first mapped by fzn0x/idx (MIT).

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

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

@@ -1,3 +1,4 @@
+pub mod ipot;
 #[cfg(feature = "testing")]
 pub mod mock;
 pub mod msn;
@@ -6,6 +7,7 @@ pub mod yahoo;
 
 use chrono::FixedOffset;
 
+use crate::broker::types::BrokerQuery;
 use crate::config::{HistoryProviderKind, ProviderKind};
 use crate::error::IdxError;
 use types::{
@@ -41,6 +43,17 @@ pub trait HistoryProvider {
     ) -> Result<Vec<Bar>, IdxError>;
 }
 
+/// Which brokers bought and sold a stock: a separate capability, served by
+/// IPOT whichever market provider is selected.
+pub trait BrokerSummaryProvider {
+    /// `code` is the bare IDX code, e.g. `BBCA`.
+    fn broker_summary(
+        &self,
+        code: &str,
+        query: &BrokerQuery,
+    ) -> Result<ipot::BrokerSummaryRaw, IdxError>;
+}
+
 pub trait FundamentalsProvider {
     fn fundamentals(&self, symbol: &str) -> Result<Fundamentals, IdxError>;
 }
@@ -258,6 +271,23 @@ fn msn_capability_error(subject: &str) -> IdxError {
     IdxError::Unsupported(format!("{subject}: command requires --provider msn"))
 }
 
+pub fn broker_provider() -> Box<dyn BrokerSummaryProvider> {
+    #[cfg(feature = "testing")]
+    if mock::enabled() {
+        return Box::new(mock::MockBrokerProvider);
+    }
+    Box::new(ipot::IpotProvider::new())
+}
+
+/// Today in WIB, the date IDX trades on.
+pub(crate) fn today_wib() -> chrono::NaiveDate {
+    #[cfg(feature = "testing")]
+    if let Some(today) = mock::today() {
+        return today;
+    }
+    chrono::Utc::now().with_timezone(&idx_offset()).date_naive()
+}
+
 /// The provider that serves history for `provider` under `history_mode`.
 pub fn history_source(provider: ProviderKind, history_mode: HistoryProviderKind) -> ProviderKind {
     match history_mode {