docs(reviewer): add ready-to-paste session prompts (S3–S6 + review gate)

session-prompts.md: one self-contained, copy-paste prompt per pending session,
each naming the model (Sonnet/Haiku/Opus), the findings + audit doc, the
build/test commands, and the branch/push/PR + review-gate workflow.  S6 carries
the G0 precondition.  Linked from finding-orchestration.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

doc/reviewer/finding-orchestration.md

@@ -13,6 +13,10 @@ know exactly what it covers and how its output gets validated.
 
 ---
 
+> **Ready-to-paste prompts** for every pending session (S3–S6 + the review gate)
+> live in [`session-prompts.md`](session-prompts.md) — copy one block, set the
+> named model, go.
+
 ## How to use this
 
 1. Pick the next **⬜ pending** session from the [sequence](#session-sequence).