refactor: rename inspect to replay across the codebase

Renames inspect-ui/ to replay-ui/, internal/inspect/ to internal/replay/,
the CLI subcommand from `sanderling inspect` to `sanderling replay`, and
updates all references in docs, Makefile, README, and Go comments.

internal/trace/writer.go

@@ -50,7 +50,7 @@ type Witness struct {
 
 // ExtractorChange records the prev/curr JSON values of an extractor whose
 // observation differed between two consecutive steps. Surfaced under
-// violation rows in the inspect UI as a "what changed at this step"
+// violation rows in the replay UI as a "what changed at this step"
 // breadcrumb.
 type ExtractorChange struct {
 	Prev json.RawMessage `json:"prev"`