fix(continuity): wire scratch-commit-before-release and rewrite bootstrap prompt (Phase 4 items 3, 5, 6)

Release now re-verifies every handoff Anchor.Dirty file hash (previously
unchecked after the top-level anchor SHA compare), snapshots dirty state
onto a per-task scratch branch before uploading, and rewrites the anchor
to the new commit so successor pickup collapses to a single HEAD compare.
ScratchCommit made idempotent for repeated rotations of the same task.

Bootstrap's prompt now points the agent at the scratch-branch commit
history instead of vague "read the handoff" prose, and does not claim a
GET /v1/artifacts/<ref> endpoint that doesn't exist.

MarkdownChanges had zero callers and zero tests; deleted per AUDIT.md's
explicit deletion option rather than half-wiring an undesigned feature.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W1rkJ2hBMybnJctPbcy4tT

cmd/orchestra/main.go

@@ -95,11 +95,11 @@ func main() {
 				}
 				switch h.Harness {
 				case "claude":
-					adapters[h.ID] = herdr.Claude(client, 200000)
+					adapters[h.ID] = herdr.Claude(client, 200000, s)
 				case "opencode":
-					adapters[h.ID] = herdr.OpenCode(client, 200000)
+					adapters[h.ID] = herdr.OpenCode(client, 200000, s)
 				case "codex", "":
-					adapters[h.ID] = herdr.Codex(client, 200000)
+					adapters[h.ID] = herdr.Codex(client, 200000, s)
 				default:
 					log.Printf("herdr %s has unsupported harness %q", h.ID, h.Harness)
 				}