Keep a condition's looks in the store, so a look that changes nothing writes no bucket (issue 420)

Every look rewrote the condition's value in the conditions bucket, because the
value carried the count of looks, the last look and the newest evidence: 131 647
writes in four days for twelve open conditions, against ADR 0289's rule that a
bucket is written only when what it describes changed. The looks now live in the
controller's store (migration 0095, condition_looks), the bucket holds what a
condition says and is written only when that changes, and the conditions verb and
the condition events put the looks back.

internal/inventory/migrations/0095-a-condition-keeps-its-looks-beside-the-bucket.sql

@@ -0,0 +1,20 @@
+-- The looks of an open condition are kept here, not in the conditions bucket (novox/hq issue 420, ADR 0289
+-- §1 and §4).
+--
+-- On 2026-10-10 the bus had stored 131 647 writes to the conditions bucket in four days while twelve
+-- conditions were open: every look rewrote a condition's value, because the value carried how many times it
+-- had been observed, when last and the newest evidence. A watcher heard a write for every look, not for
+-- every change. The bucket now holds what a condition says, written when that changes; how often and when
+-- it was last seen, and what each look said, change on every look and are kept in this row, written by the
+-- serving controller under its lease (`epoch`) and read back by `conditions` and the events it says.
+--
+-- One row per open condition, removed when it clears. `evidence` is the newest observations, newest first,
+-- as the condition's `evidence` says them: [{"at", "said"}].
+create table condition_looks (
+    key           text        primary key,
+    observations  integer     not null check (observations >= 0),
+    last_observed timestamptz not null,
+    evidence      jsonb       not null default '[]',
+    epoch         bigint,
+    kept_at       timestamptz not null default now()
+);