feat: live PDF preview, upload-to-branch diff, and copy markdown per branch

- Backend: authenticated GET preview endpoint generates PDF on-demand from any
  version without requiring a public asset publish
- Backend: POST upload endpoint on a version accepts a .docx, parses it to
  structured blocks, diffs against current blocks, and records patches
- Frontend: new Preview tab shows live PDF rendered from the authenticated
  endpoint (blob URL via fetch with auth header)
- Frontend: Upload DOCX (arrow-up) button in action bar sends the file to the
  branch, backend computes diff automatically
- Frontend: Copy Markdown button (clipboard icon) appears on branch hover in
  CVTree; copies block path/type/text as structured markdown to clipboard

https://claude.ai/code/session_01BTNfDfgFvcnehkve6r66nk

apps/backend/fastapi/app/services/versions.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from fastapi import UploadFile
 from sqlalchemy import delete, select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
@@ -8,11 +9,34 @@ from dlib.cv import (
     StructuredBlock,
     StructuredDocument,
     PatchPayload,
+    PatchOperation,
     apply_patchset,
     validate_patchset,
+    parse_docx_bytes,
 )
 
 from app.models import CvDocument, CvPatch, CvVersion, PublicAsset
+from app.services.storage import persist_upload
+
+
+def _diff_blocks(old: list[dict], new: list[dict]) -> list[PatchPayload]:
+    old_map = {b["path"]: b for b in old}
+    new_map = {b["path"]: b for b in new}
+    patches: list[PatchPayload] = []
+    for path, nb in new_map.items():
+        ob = old_map.get(path)
+        if ob and ob["text"] != nb["text"]:
+            patches.append(PatchPayload(
+                target_path=path, operation=PatchOperation.REPLACE_TEXT,
+                old_value=ob["text"], new_value=nb["text"],
+            ))
+    for path, ob in old_map.items():
+        if path not in new_map and ob.get("block_type") != "heading":
+            patches.append(PatchPayload(
+                target_path=path, operation=PatchOperation.REMOVE_BLOCK,
+                old_value=ob["text"],
+            ))
+    return patches
 
 
 async def create_branch(
@@ -153,6 +177,55 @@ async def append_patches_to_version(
     return result.scalars().one()
 
 
+async def upload_docx_to_version(
+    session: AsyncSession,
+    *,
+    owner_id: str,
+    version_id: str,
+    upload: UploadFile,
+) -> CvVersion | None:
+    stmt = (
+        select(CvVersion)
+        .join(CvVersion.document)
+        .where(CvVersion.id == version_id, CvDocument.owner_id == owner_id)
+        .options(selectinload(CvVersion.patches), selectinload(CvVersion.public_assets))
+    )
+    version = (await session.execute(stmt)).scalars().one_or_none()
+    if not version:
+        return None
+
+    artifact_key, file_bytes = await persist_upload(upload, owner_id)
+    new_blocks_parsed = parse_docx_bytes(file_bytes)
+    new_blocks = [b.model_dump() for b in new_blocks_parsed.blocks]
+
+    diff_patches = _diff_blocks(version.structured_blocks or [], new_blocks)
+
+    version.artifact_docx_key = artifact_key
+    version.structured_blocks = new_blocks
+    metadata = version.metadata_json or {}
+    metadata["patch_count"] = int(metadata.get("patch_count") or 0) + len(diff_patches)
+    version.metadata_json = metadata
+
+    for patch in diff_patches:
+        session.add(CvPatch(
+            version_id=version.id,
+            target_path=patch.target_path,
+            operation=patch.operation.value,
+            old_value=patch.old_value,
+            new_value=patch.new_value,
+            metadata_json=patch.metadata,
+        ))
+
+    await session.commit()
+
+    stmt_refresh = (
+        select(CvVersion)
+        .where(CvVersion.id == version_id)
+        .options(selectinload(CvVersion.patches), selectinload(CvVersion.public_assets))
+    )
+    return (await session.execute(stmt_refresh)).scalars().one()
+
+
 async def delete_version(
     session: AsyncSession, owner_id: str, version_id: str
 ) -> bool | str: