feat(author): add continuation-mode selection wall for open-PR issues (#188)

Issues already represented by open PRs must not be selected for fresh work
unless the operator explicitly requests continuation. Adds classification,
continuation report proofs (old/new head SHA, PR author, branch), contradictory
no-PR claim detection, and edited-PR inventory coverage checks.

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

skills/llm-project-workflow/SKILL.md

@@ -379,6 +379,12 @@ Role-specific fields (append to the compact block):
   `Linked issue status:`, `Cleanup status:`
 - author tasks: `Selected issue:`, `Claim/comment status:`,
   `PR number opened:`, `No review/merge:` (explicit confirmation)
+- continuation tasks (#188): `Continuation mode:`, `Existing PR:`,
+  `PR author:`, `Branch:`, `Old PR head:`, `New PR head:`,
+  `Session authored PR:`, `Why continuation allowed:` — issues with open
+  PRs are excluded from fresh selection unless operator explicitly requests
+  continuation (`review_proofs.classify_issue_for_selection`,
+  `assess_issue_selection_final_report`)
 - queue/inventory tasks: `Repositories checked:`, `Open PR counts:`,
   `Selected PR or reason none selected:`, `Inventory completeness:`