Close citation/source living-person leak; add on-demand tree purge

Two changes.

1. Privacy fix (NN#2/NN#3) — the citation and source list endpoints gated only
   on can_view_tree, so a non-member on a public/unlisted/site_members tree could
   enumerate citations and sources tied to a redacted living person, leaking that
   the person exists and has sourced facts (and possibly their name via a source
   title). #46 closed this for events/media/names/relationships but not
   citations/sources. Now citation_service.list_citations and
   source_service.{list_sources,get_source} delegate non-member reads to
   public_view_service, mirroring the #46 pattern:
   - citations: shown only when the cited fact resolves to FULL-visibility
     person(s) — covers the person_id, name_id, event_id (person or both-partner),
     and relationship_id (both-partner) target paths.
   - sources: shown only when they back at least one visible citation; a withheld
     source 404s (don't reveal it exists).
   Tests cover all four citation target types + source withholding + member-sees-all.

2. On-demand tree purge — owners can permanently delete a soft-deleted tree now
   instead of waiting out the 30-day auto-purge window. POST /trees/{id}/purge
   (owner-only): the tree must already be in the trash, and the caller retypes its
   name to confirm. Media objects are deleted from storage, then a single
   DELETE on trees cascades all tree-owned rows via the tree_id ON DELETE CASCADE;
   the audit entry survives (tree_id SET NULL). Frontend adds a "Delete forever"
   button to the Recently-deleted list. No migration.

Suite: 102 passing.
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/api/v1/trees.py

@@ -2,8 +2,8 @@ import uuid
 
 from fastapi import APIRouter, status
 
-from app.api.deps import CurrentUser, SessionDep
-from app.schemas.tree import TreeCreate, TreeRead, TreeUpdate
+from app.api.deps import CurrentUser, ObjectStoreDep, SessionDep
+from app.schemas.tree import TreeCreate, TreePurge, TreeRead, TreeUpdate
 from app.services import tree_service
 
 router = APIRouter(prefix="/trees", tags=["trees"])
@@ -57,3 +57,18 @@ async def delete_tree(tree_id: uuid.UUID, session: SessionDep, current: CurrentU
 async def restore_tree(tree_id: uuid.UUID, session: SessionDep, current: CurrentUser) -> TreeRead:
     tree = await tree_service.restore_tree(session, actor=current, tree_id=tree_id)
     return TreeRead.model_validate(tree)
+
+
+@router.post("/{tree_id}/purge", status_code=status.HTTP_204_NO_CONTENT)
+async def purge_tree(
+    tree_id: uuid.UUID,
+    data: TreePurge,
+    session: SessionDep,
+    current: CurrentUser,
+    store: ObjectStoreDep,
+) -> None:
+    """Permanently delete a soft-deleted tree and all its data — irreversible.
+    Owner-only; the tree must be in the trash and `confirm_name` must match."""
+    await tree_service.purge_tree(
+        session, store, actor=current, tree_id=tree_id, confirm_name=data.confirm_name
+    )