feat: require validation cwd and HEAD proof in reviewer reports (Closes #398)

Add assess_validation_cwd_proof_report so reviewer final reports must prove
pwd, git rev-parse HEAD, git status, and expected PR head SHA before
claiming validation ran in a branches/ worktree. Wire the verifier into
final_report_validator and gitea_validate_review_final_report.

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

skills/llm-project-workflow/workflows/review-merge-pr.md

@@ -574,6 +574,28 @@ Do not claim “full-suite failures are pre-existing” unless baseline proof is
 
 ## 23. Validation command proof rule
 
+Before any diff, test, or compile validation, record in the same command
+transcript or final report:
+
+* `pwd` or explicit working directory
+* `git rev-parse HEAD`
+* `git status --short --branch`
+* expected PR head SHA (candidate head SHA)
+
+Validation commands must use one of:
+
+* `git -C <review_worktree> ...`
+* `cd <review_worktree> && ...` in the same command
+* tool-provided explicit working-directory metadata
+
+Do not rely on inferred shell cwd from a prior command in a different block.
+
+`gitea_validate_review_final_report` rejects validation claims without
+cwd/HEAD proof when `validation_session` is supplied.
+
+Baseline validation must document baseline worktree path, baseline target SHA,
+cwd proof, exact baseline command, and baseline result using the same rules.
+
 Report the exact validation command as executed.
 
 Report the working directory where validation ran.
@@ -1096,6 +1118,7 @@ Controller Handoff:
 * Baseline worktree path:
 * Files reviewed:
 * Validation:
+* Validation cwd/HEAD proof:
 * Official validation integrity status:
 * Terminal review mutation:
 * Review decision: