Sprint 2 : moteur de documents + sanctuaire

Backend:
- CRUD complet documents/items/versions (update, delete, accept, reject, reorder)
- Service IPFS (upload/retrieve/pin via kubo HTTP API)
- Service sanctuaire : pipeline SHA-256 + IPFS + on-chain (system.remark)
- Verification integrite des entrees sanctuaire
- Recherche par reference (document -> entrees sanctuaire)
- Serialisation deterministe des documents pour archivage
- 14 tests unitaires supplementaires (document service)

Frontend:
- 9 composants : StatusBadge, MarkdownRenderer, DiffView, ItemCard,
  ItemVersionDiff, DocumentList, SanctuaryEntry, IPFSLink, ChainAnchor
- Page detail item avec historique des versions et diff
- Page detail sanctuaire avec verification integrite
- Modal de creation de document + proposition de version
- Archivage document vers sanctuaire depuis la page detail

Documentation:
- API reference mise a jour (9 nouveaux endpoints)
- Guides utilisateur documents et sanctuaire enrichis

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/services/ipfs_service.py

@@ -0,0 +1,125 @@
+"""IPFS service: upload, retrieve, and pin content via kubo HTTP API.
+
+Uses httpx async client to communicate with the local kubo node.
+All operations handle connection errors gracefully: they log a warning
+and return None instead of crashing the caller.
+"""
+
+from __future__ import annotations
+
+import logging
+
+import httpx
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+# Timeout for IPFS operations (seconds)
+_IPFS_TIMEOUT = 30.0
+
+
+async def upload_to_ipfs(content: str | bytes) -> str | None:
+    """Upload content to IPFS via kubo HTTP API (POST /api/v0/add).
+
+    Parameters
+    ----------
+    content:
+        The content to upload. Strings are encoded as UTF-8.
+
+    Returns
+    -------
+    str | None
+        The IPFS CID (Content Identifier) of the uploaded content,
+        or None if the upload failed.
+    """
+    if isinstance(content, str):
+        content = content.encode("utf-8")
+
+    try:
+        async with httpx.AsyncClient(timeout=_IPFS_TIMEOUT) as client:
+            response = await client.post(
+                f"{settings.IPFS_API_URL}/api/v0/add",
+                files={"file": ("content.txt", content, "application/octet-stream")},
+            )
+            response.raise_for_status()
+            data = response.json()
+            cid = data.get("Hash")
+            if cid:
+                logger.info("Contenu uploade sur IPFS: CID=%s", cid)
+            return cid
+    except httpx.ConnectError:
+        logger.warning("Impossible de se connecter au noeud IPFS (%s)", settings.IPFS_API_URL)
+        return None
+    except httpx.HTTPStatusError as exc:
+        logger.warning("Erreur HTTP IPFS lors de l'upload: %s", exc.response.status_code)
+        return None
+    except Exception:
+        logger.warning("Erreur inattendue lors de l'upload IPFS", exc_info=True)
+        return None
+
+
+async def get_from_ipfs(cid: str) -> bytes | None:
+    """Retrieve content from IPFS by CID via the gateway.
+
+    Parameters
+    ----------
+    cid:
+        The IPFS Content Identifier to retrieve.
+
+    Returns
+    -------
+    bytes | None
+        The raw content bytes, or None if retrieval failed.
+    """
+    try:
+        async with httpx.AsyncClient(timeout=_IPFS_TIMEOUT) as client:
+            response = await client.post(
+                f"{settings.IPFS_API_URL}/api/v0/cat",
+                params={"arg": cid},
+            )
+            response.raise_for_status()
+            logger.info("Contenu recupere depuis IPFS: CID=%s", cid)
+            return response.content
+    except httpx.ConnectError:
+        logger.warning("Impossible de se connecter au noeud IPFS (%s)", settings.IPFS_API_URL)
+        return None
+    except httpx.HTTPStatusError as exc:
+        logger.warning("Erreur HTTP IPFS lors de la recuperation (CID=%s): %s", cid, exc.response.status_code)
+        return None
+    except Exception:
+        logger.warning("Erreur inattendue lors de la recuperation IPFS (CID=%s)", cid, exc_info=True)
+        return None
+
+
+async def pin(cid: str) -> bool:
+    """Pin content on the local IPFS node to prevent garbage collection.
+
+    Parameters
+    ----------
+    cid:
+        The IPFS Content Identifier to pin.
+
+    Returns
+    -------
+    bool
+        True if pinning succeeded, False otherwise.
+    """
+    try:
+        async with httpx.AsyncClient(timeout=_IPFS_TIMEOUT) as client:
+            response = await client.post(
+                f"{settings.IPFS_API_URL}/api/v0/pin/add",
+                params={"arg": cid},
+            )
+            response.raise_for_status()
+            logger.info("Contenu epingle sur IPFS: CID=%s", cid)
+            return True
+    except httpx.ConnectError:
+        logger.warning("Impossible de se connecter au noeud IPFS pour l'epinglage (%s)", settings.IPFS_API_URL)
+        return False
+    except httpx.HTTPStatusError as exc:
+        logger.warning("Erreur HTTP IPFS lors de l'epinglage (CID=%s): %s", cid, exc.response.status_code)
+        return False
+    except Exception:
+        logger.warning("Erreur inattendue lors de l'epinglage IPFS (CID=%s)", cid, exc_info=True)
+        return False