Let a pinned minute read runs from the whole day

/observability/runs gains since/until, so the throughput chart's pin asks
the server for its minute instead of filtering a fixed recent list. This
engine writes ~60 runs a minute, so any minute but the newest read empty.

since is inclusive and until exclusive, matching the minute buckets the
charts are drawn from. Hover stays the client-side preview it was:
scrubbing a day would otherwise be a request per minute rested on.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017MeiWk3Yq12n2pTvnQWYvt

NOTEPAD.md

@@ -51,7 +51,6 @@ is what M4 still waits on, together with porting the flows.
 - CHORE/API: the metrics collector is a bus subscriber, so a storm that overflows the bus queue undercounts. The events dropped are the same ones the websocket drops; exact accounting would need the collector to be fed from the engine rather than the bus.
 - CHORE/API: `/observability/summary` reports the work queue's `depth` as the Redis stream length, which is the journal size (capped at `STREAM_MAXLEN`) rather than a backlog. The health screen shows `pending` instead; the field name still invites the wrong reading.
 - FEAT/UI: the health screen's window is fixed at 24 hours and the charts fold minute buckets in Python. A range picker (and `date_bin()` behind it) is the next step if anyone wants a week.
-- FEAT/API: `/observability/runs` takes no time range and caps at 200 rows, so picking a minute on the throughput chart can only filter the runs the list happens to hold — on a busy engine that is its last minute or so, and any earlier minute reads as empty. A `since`/`until` parameter would let a moment on a chart reach the whole day. Failures are sparse enough that the same pairing works there.
 - CHORE/FLOW: run records for a deleted flow stay until the retention window passes, so a flow that no longer exists keeps appearing in the history. Deliberate — it is a record of what ran — but `forget_flow` could offer to clear it.
 - CHORE/API: nothing can ask the collector to flush now, so anything needing the tables to be current has to wait out `FLUSH_INTERVAL_S` — which is what the soak harness does before clearing its own rows.
 - BUG/UI: `MemoryWorkQueue.stats()` hard-codes `pending: 0`, so the health tile always reads zero on a stack without Redis.