feat: add canonical state handoff ledger (#494)

Add templates, validators, and documentation for discussion/issue/PR state
comments and final-report next-action handoff fields. Wire enforcement into
assess_final_report_validator across all workflow task kinds.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_final_report_validator.py

@@ -35,6 +35,9 @@ def _review_handoff(**overrides):
         "- External-state mutations: none",
         "- Read-only diagnostics: issue and PR metadata inspected",
         "- Current status: PR open",
+        "- Next actor: author",
+        "- Next action: address review feedback",
+        "- Next prompt: Fix PR #203 per reviewer request_changes and push updated head",
         "- Blockers: none",
         "- Next: await author",
         "- Safety: no self-review; no self-merge",
@@ -92,6 +95,9 @@ def _reconcile_handoff(drop=(), **overrides):
         "- Read-only diagnostics: gitea_view_pr, gitea_view_issue",
         "- Reconciliation mutations: PR comment posted",
         "- Current status: reconciliation complete",
+        "- Next actor: reconciler",
+        "- Next action: close PR #99 after capability proof",
+        "- Next prompt: Reconcile already-landed PR #99 with prgs-reconciler profile",
         "- Blocker: missing gitea.pr.close capability",
         "- Safe next action: hand off to a profile with gitea.pr.close",
         "- No review/merge confirmation: confirmed",