feat(iace): DSMS-CID-Badge im Tech-File-Export + aggregierter Bulk-Diff

Punkt 1 — UI-CID-Badge nach erfolgreichem Tech-File-Export:
- archiveTechFile setzt X-DSMS-CID / X-DSMS-Filename / X-DSMS-Size response
  headers + Access-Control-Expose-Headers, sobald DSMS-Archive durchlief
- Split iace_handler_techfile.go (war ueber 500 LOC) → archiveTechFile lebt
  jetzt in iace_handler_techfile_archive.go, setDSMSResponseHeaders als
  pure Helper mit 3 unit tests
- Next.js IACE-Proxy forwarded die X-DSMS-* Header und erkennt jetzt auch
  XLSX/DOCX/MD als Binary-Response (vorher nur PDF/ZIP/octet-stream)
- ExportCIDBadge.tsx zeigt CID, Filename, Groesse + Kopieren-Button +
  "Verlauf anzeigen" (oeffnet CIDHistoryModal)

Punkt 2 — Bulk-Diff Report V1 → V_latest:
- Neuer Endpoint GET /api/v1/documents/{cid}/bulk-diff im dsms-gateway:
  laeuft parent_cid-Kette ab, berechnet chronologische Step-Diffs,
  aggregiert Totals (added/removed lines, metadata_fields_changed,
  binary_steps). Edge-Cases: einzelne Version, binaere Steps, abgebrochene
  Kette
- BulkDiffPanel.tsx zeigt 4-Stat-Header + Step-Tabelle
- CIDHistoryModal bekommt Toggle-Button "Bulk-Diff V1 → V_latest anzeigen"
  neben dem Versions-Counter; damit auch vom IACE-Export-Badge erreichbar

Tests: 3 neue Go-Tests, 4 neue pytest-Tests, alle gruen

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dsms-gateway/routers/documents.py

@@ -343,6 +343,108 @@ async def diff_documents(cid_a: str, cid_b: str):
     }
 
 
+@router.get("/api/v1/documents/{cid}/bulk-diff")
+async def bulk_diff_chain(cid: str):
+    """
+    Aggregate diff across the entire parent_cid chain (V1 → V_latest).
+
+    Walks the history chain once, then computes per-step diffs between every
+    chronological pair plus running totals. Designed for the "Bulk-Diff
+    Report" panel in the IACE audit timeline so the user can see how a
+    tech-file evolved across all versions without clicking each pair.
+    """
+    history: list[dict] = []
+    current_cid: Optional[str] = cid
+    max_depth = 50
+
+    for _ in range(max_depth):
+        if current_cid is None:
+            break
+        try:
+            raw = await ipfs_cat(current_cid)
+            package = json.loads(raw)
+        except Exception:
+            break
+        metadata = package.get("metadata", {}) or {}
+        history.append({
+            "cid": current_cid,
+            "version": metadata.get("version"),
+            "created_at": metadata.get("created_at"),
+            "metadata": metadata,
+            "package": package,
+        })
+        parent = metadata.get("parent_cid")
+        if not parent or parent == current_cid:
+            break
+        current_cid = parent
+
+    if len(history) < 2:
+        return {
+            "cid_latest": cid,
+            "cid_baseline": cid,
+            "versions": len(history),
+            "steps": [],
+            "totals": {"added_lines": 0, "removed_lines": 0, "metadata_fields_changed": 0, "binary_steps": 0},
+            "note": "No predecessor versions found." if history else "CID not found.",
+        }
+
+    # history is newest→oldest; reverse to walk chronologically.
+    chronological = list(reversed(history))
+    steps: list[dict] = []
+    total_added = 0
+    total_removed = 0
+    binary_steps = 0
+    fields_changed: set[str] = set()
+
+    for i in range(len(chronological) - 1):
+        older = chronological[i]
+        newer = chronological[i + 1]
+        meta_diff = _diff_metadata(older["metadata"], newer["metadata"])
+        text_a, text_b, is_binary = _extract_texts(older["package"], newer["package"])
+
+        step: dict = {
+            "from": older["cid"],
+            "from_version": older["version"],
+            "to": newer["cid"],
+            "to_version": newer["version"],
+            "created_at": newer["created_at"],
+            "metadata_diff_fields": sorted(meta_diff.keys()),
+        }
+
+        if is_binary:
+            step["kind"] = "binary"
+            step["added_lines"] = 0
+            step["removed_lines"] = 0
+            binary_steps += 1
+        else:
+            diff_lines = list(
+                _unified_diff(text_a.splitlines(), text_b.splitlines(), fromfile=older["cid"], tofile=newer["cid"], lineterm="")
+            )
+            added = sum(1 for ln in diff_lines if ln.startswith("+") and not ln.startswith("+++"))
+            removed = sum(1 for ln in diff_lines if ln.startswith("-") and not ln.startswith("---"))
+            step["kind"] = "text"
+            step["added_lines"] = added
+            step["removed_lines"] = removed
+            total_added += added
+            total_removed += removed
+
+        fields_changed.update(meta_diff.keys())
+        steps.append(step)
+
+    return {
+        "cid_latest": cid,
+        "cid_baseline": chronological[0]["cid"],
+        "versions": len(history),
+        "steps": steps,
+        "totals": {
+            "added_lines": total_added,
+            "removed_lines": total_removed,
+            "metadata_fields_changed": len(fields_changed),
+            "binary_steps": binary_steps,
+        },
+    }
+
+
 def _diff_metadata(a: dict, b: dict) -> dict:
     """Return per-field change list: {field: {"old": ..., "new": ...}}."""
     keys = set(a.keys()) | set(b.keys())