docs(linkedin-studio): RE-R3e — Nytt-siden-sist header carries the prior date (plan/brief fidelity)

The shipped render dates the section header (## 🆕 Nytt siden sist (<prior-date>))
when a prior brief exists — the form SC9, Phase-B, and the behavioural step already
specify. The plan Step 3 snippet showed a bare header and the brief S-history prose
was silent on the date; both are corrected to match the shipped code.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011vmzxpsFpc8q19LaogAWLD

docs/research-engine/brief-re-r3e.md

@@ -130,7 +130,8 @@ to wire into the gate), its unit tests in `brief.test.ts`, its CLI wiring (prior
   - **Frontmatter `surfaced:` line** — `surfaced: ${surfacedIds(ranking).join(",")}` inserted **before**
     `schemaVersion:` (always emitted, even for an empty store → `surfaced: ` blank; this is the record the *next*
     day's diff reads, independent of whether *today* had a prior). `schemaVersion:` now renders **2**.
-  - **A `## 🆕 Nytt siden sist` section**, placed **after the intro line and before `## 🎯 Topp-treff`** (the
+  - **A `## 🆕 Nytt siden sist` section** (the header gains ` (<prior-date>)` when a prior brief exists, per SC9),
+    placed **after the intro line and before `## 🎯 Topp-treff`** (the
     delta leads, then the full ranked list). Branches (all deterministic):
     - **no diff arg / `priorDate === null` with added** → `_Første brief — alt nedenfor er nytt._`
     - **`priorDate === null` with no added** (empty first brief) → `_Første brief._`

docs/research-engine/plan-re-r3e.md

@@ -173,7 +173,7 @@ Make the Phase-A diff/parse/select cases green.
     `schemaVersion:` line now renders `2` via the bumped constant.
   - After the intro line (`brief.ts:273-276`) and **before** `## 🎯 Topp-treff` (`:278`), emit the section:
     ```ts
-    lines.push("## 🆕 Nytt siden sist");
+    lines.push(diff.priorDate !== null ? `## 🆕 Nytt siden sist (${diff.priorDate})` : "## 🆕 Nytt siden sist");
     if (diff.priorDate === null) {
       lines.push(diff.added.length > 0 ? "_Første brief — alt nedenfor er nytt._" : "_Første brief._", "");
     } else if (diff.added.length === 0) {