feat(repos): multi-machine path support via host_paths

Adds a JSONB column `host_paths` to managed_repos mapping
hostname → absolute local path. Fixes the consistency-checker
failure when the same repo lives at different paths on different
machines (e.g. /home/worsch/marki-docx on the workstation vs
/home/tegwick/marki-docx on custodiancore).

Changes:
- Migration g4b5c6d7e8f9: adds host_paths JSONB (default {})
- Model: host_paths Mapped[dict] column
- Schemas: host_paths in RepoRead; new RepoPathRegister schema
- Router: POST /repos/{slug}/paths/ — merges one host entry
- consistency_check.py: resolve_repo_path() prefers host_paths
  [hostname] over local_path; --repo-path CLI override added
- MCP: update_repo_path(slug, path, host?) tool
- Makefile: register-path target; REPO_PATH passthrough on
  check-consistency and fix-consistency targets
- TOOLS.md: documents update_repo_path

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

api/routers/repos.py

@@ -15,6 +15,7 @@ from api.schemas.managed_repo import (
     DispatchWorkstream,
     RepoCreate,
     RepoDispatch,
+    RepoPathRegister,
     RepoRead,
     RepoUpdate,
 )
@@ -89,6 +90,26 @@ async def update_repo(
     return repo
 
 
+@router.post("/{slug}/paths/", response_model=RepoRead)
+async def register_host_path(
+    slug: str,
+    body: RepoPathRegister,
+    session: AsyncSession = Depends(get_session),
+) -> ManagedRepo:
+    """Register or update the local path for a specific host.
+
+    Merges {"host": path} into host_paths without overwriting other entries.
+    Use this when a repo lives at a different absolute path on different machines.
+    """
+    repo = await _get_repo_by_slug(slug, session)
+    updated = dict(repo.host_paths or {})
+    updated[body.host] = body.path
+    repo.host_paths = updated
+    await session.commit()
+    await session.refresh(repo)
+    return repo
+
+
 @router.patch("/{slug}/archive", response_model=RepoRead)
 async def archive_repo(
     slug: str,