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/mock.rs

@@ -2,7 +2,10 @@
 //! `IDX_USE_MOCK_PROVIDER`. Release builds do not contain it.
 
 use super::types::{Bar, Fundamentals, Interval, Period, Quote};
-use super::{FundamentalsProvider, HistoryProvider, QuoteProvider, msn, yahoo};
+use super::{
+    BrokerSummaryProvider, FundamentalsProvider, HistoryProvider, QuoteProvider, ipot, msn, yahoo,
+};
+use crate::broker::types::{BrokerBoard, BrokerInvestor, BrokerQuery};
 use crate::config::ProviderKind;
 use crate::error::IdxError;
 
@@ -10,6 +13,15 @@ pub(crate) fn enabled() -> bool {
     std::env::var("IDX_USE_MOCK_PROVIDER").is_ok()
 }
 
+/// `IDX_MOCK_TODAY` (YYYY-MM-DD) pins today's date under the mock provider.
+pub(crate) fn today() -> Option<chrono::NaiveDate> {
+    if !enabled() {
+        return None;
+    }
+    let raw = std::env::var("IDX_MOCK_TODAY").ok()?;
+    chrono::NaiveDate::parse_from_str(&raw, "%Y-%m-%d").ok()
+}
+
 pub struct MockProvider {
     quote: Result<Quote, IdxError>,
     fundamentals: Result<Fundamentals, IdxError>,
@@ -117,3 +129,38 @@ impl HistoryProvider for MockProvider {
         self.history.clone()
     }
 }
+
+/// Broker summaries from `tests/fixtures/ipot_brokersummary_<code>_<from>
+/// [_<to>][_<investor>_<board>].html`; a query without a fixture reads as an
+/// unknown code.
+pub struct MockBrokerProvider;
+
+impl BrokerSummaryProvider for MockBrokerProvider {
+    fn broker_summary(
+        &self,
+        code: &str,
+        query: &BrokerQuery,
+    ) -> Result<ipot::BrokerSummaryRaw, IdxError> {
+        if std::env::var("IDX_MOCK_ERROR").is_ok() {
+            return Err(IdxError::ProviderUnavailable);
+        }
+        let mut name = format!(
+            "ipot_brokersummary_{}_{}",
+            code.to_ascii_lowercase(),
+            query.from.format("%Y%m%d")
+        );
+        if query.to != query.from {
+            name.push_str(&query.to.format("_%Y%m%d").to_string());
+        }
+        if (query.investor, query.board) != (BrokerInvestor::All, BrokerBoard::All) {
+            name.push_str(&format!(
+                "_{}_{}",
+                query.investor.as_str(),
+                query.board.as_str()
+            ));
+        }
+        let html = std::fs::read_to_string(format!("tests/fixtures/{name}.html"))
+            .unwrap_or_else(|_| "Invalid stock code!".to_string());
+        ipot::summary_from_html(code, &html)
+    }
+}