perf(ingest,cli): derive archive bounds from the monthly file index — probe_window drain retired

probe_window drained a source's entire close column just to learn its
first and last bar timestamp; both live callers (open_real_source and
campaign_window_ms on the campaign trunk) now resolve through
aura-ingest's new archive_extent(): list the symbol's SYM_YYYY_MM.m1
files, load only the boundary months via the existing loader seam, and
walk across gap months forward/backward — O(2 file loads) typical
instead of O(archive). Empty-window refusal semantics are unchanged
(pinned). Two characterization tests captured the resolved windows
against the OLD implementation over the synthetic per-test archive and
stay green unchanged after the swap.

Measured: the probe itself drops 366ms -> 13ms (~28x) on the full
2014-2026 GER40 archive; end-to-end command wall-clock moves only
~2-3% because the sim loop dominates — the fix removes an
O(archive-size) term, not the dominant cost.

closes #252

crates/aura-cli/src/main.rs

@@ -620,17 +620,8 @@ fn probe_window(
     to_ms: Option<i64>,
     env: &project::Env,
 ) -> (Timestamp, Timestamp) {
-    let mut probe = aura_ingest::open_columns(server, symbol, from_ms, to_ms, &[aura_ingest::M1Field::Close])
+    aura_ingest::archive_extent(server, std::path::Path::new(&env.data_path()), symbol, from_ms, to_ms)
         .unwrap_or_else(|| no_data_in_window(symbol, from_ms, to_ms, env))
-        .pop()
-        .expect("open_columns yields one source per requested field");
-    let first =
-        aura_engine::Source::peek(probe.as_ref()).unwrap_or_else(|| no_data_in_window(symbol, from_ms, to_ms, env));
-    let mut last = first;
-    while let Some((t, _)) = aura_engine::Source::next(&mut *probe) {
-        last = t;
-    }
-    (first, last)
 }
 
 /// Open the real M1 sources for a recorded symbol over an optional window — one