fix(std): snap time-bucket/session reads to the nominal minute

Provider M1 stamps carry sub-second jitter around minute boundaries
(~55% of days stamp the 09:00 Berlin bar at 08:59:59.xxx), so any
consumer dividing or truncating the raw stamp mis-buckets boundary
bars: Resample and VolTfStop fold the bar into the previous bucket
instead of rolling over, Session demotes the first in-session bar to
at-open.

Fix per the decision logged on the issue: one shared
Timestamp::snap_to_nearest_minute in aura-core (round-half-up,
rem_euclid so negative epochs snap correctly), applied consumer-side
at the three membership computations. The recorded stream stays
byte-verbatim — no ingestion rewrite, record-then-replay untouched;
an ingestion-time rewrite was rejected because it would hide the raw
time axis from every consumer and could reorder the k-way merge
around boundaries.

Verified: the three formerly-RED tests pass individually; full
workspace suite green; clippy clean.

closes #280

crates/aura-std/src/resample.rs

@@ -104,7 +104,7 @@ impl Node for Resample {
     fn eval(&mut self, ctx: Ctx<'_>) -> Option<&[Cell]> {
         // Barrier(0) guarantees all four arrive co-fresh; read the newest M1.
         let (o, h, l, c) = (ctx.f64_in(0)[0], ctx.f64_in(1)[0], ctx.f64_in(2)[0], ctx.f64_in(3)[0]);
-        let bucket = ctx.now().0 / self.period_ns;
+        let bucket = ctx.now().snap_to_nearest_minute().0 / self.period_ns;
 
         match self.acc.take() {
             // first ever sample: start the accumulator, nothing complete yet.

crates/aura-std/src/session.rs

@@ -118,7 +118,7 @@ impl Node for Session {
         // tz-aware LOCAL wall-clock — chrono-tz applies the correct
         // DST offset for this date, so the same local minute reads the same bar
         // index in summer (CEST) and winter (CET).
-        let local = self.tz.timestamp_nanos(ctx.now().0);
+        let local = self.tz.timestamp_nanos(ctx.now().snap_to_nearest_minute().0);
         let mins = local.hour() as i64 * 60 + local.minute() as i64 - self.open_minutes;
         // i64 division: in-session closes land on exact period boundaries, so the
         // value is the bar index; pre-open is <= 0 (non-actionable).

crates/aura-std/src/vol_tf_stop.rs

@@ -90,7 +90,7 @@ impl Node for VolTfStop {
             return None; // fire with price (warm-up filter)
         }
         let price = w[0];
-        let bucket = ctx.now().0 / self.period_ns;
+        let bucket = ctx.now().snap_to_nearest_minute().0 / self.period_ns;
         match self.bucket {
             // First ever sample: open the accumulator, nothing complete yet.
             None => {