Collapse a pane name's task id in an observation signature

The ledger's first live run showed it: a pane name carries the task id in
lower case, so "phase rotation ...: pane orchestra-<task>-<sha>:1.0 still
holds input" signed differently on every task and could never accumulate
recurrence across them. The id pattern is case-insensitive now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVbaKucEYBjMqVeUgJUsc1

internal/domain/observation.go

@@ -90,7 +90,11 @@ func (i ObservationIncident) Key() string {
 }
 
 var (
-	observationID       = regexp.MustCompile(`\b[0-9A-HJKMNP-TV-Z]{26}\b`)
+	// Case-insensitive: a task id appears upper-case in a message and
+	// lower-case inside a pane name, and the live ledger's first run showed
+	// pane names keeping their task, which would give the same failure a
+	// different signature on every task.
+	observationID       = regexp.MustCompile(`(?i)\b[0-9A-HJKMNP-TV-Z]{26}\b`)
 	observationSHA      = regexp.MustCompile(`\b[0-9a-f]{7,64}\b`)
 	observationDuration = regexp.MustCompile(`\b\d+(\.\d+)?(ns|us|µs|ms|s|m|h)(\d+(\.\d+)?(ns|us|µs|ms|s|m|h))*\b`)
 	observationNumber   = regexp.MustCompile(`\b\d+\b`)