refactor(core): open AppDataStores instead of exporting SqlitePool

Introduce persistence::open_all so domain stores (invitation, targeted,
blocked) are constructed once. Extract TargetedTransferStore and own it on
CoreInner; soft-close raw pool access for new callers.

Co-authored-by: Cursor <cursoragent@cursor.com>

CONTEXT.md

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+# VniDrop
+
+Local peer-to-peer file transfer. This glossary is the product/core ubiquitous language — not an implementation guide.
+
+## Transfers
+
+**Invitation transfer**:
+A share anyone with the ticket can request, subject to approval and access policy. Ordinary multi-recipient send/receive.
+_Avoid_: contact send, held offer, reusable share offer
+
+**Targeted transfer**:
+A transfer bound to one saved-device relationship: immutable sender, receiver, manifest, and content identity; requires explicit approval before content.
+_Avoid_: contact transfer, private share
+
+**Saved device**:
+A remote app identity this installation has mutually consented to remember, with directional grants at a relationship generation.
+_Avoid_: contact, person, account
+
+**Device relationship**:
+The durable pairing state between this installation and a remote endpoint (pending, saved, forgotten/blocked lifecycle).
+_Avoid_: contact record, friendship
+
+## Persistence (core)
+
+**Domain store**:
+The module that owns schema and queries for one domain (invitation history, targeted transfers, blocked devices, relationship rows, secret metadata). Callers use store methods — never a raw SQL pool.
+_Avoid_: repository-for-everything, DAO, database layer
+
+**Invitation repository**:
+The domain store for invitation-transfer history, artifacts, receiver requests, and related events. Today’s type name may still be `Repository`.
+_Avoid_: “the database”, AppDataStores
+
+**AppDataStores**:
+The bag of concrete domain stores opened together for one app-data profile (one SQLite pool, every schema applied once).
+_Avoid_: Repository (for the bag), Persistence (as a type name), DbContext
+
+**Persistence open**:
+Creating the profile’s SQLite pool, applying all domain schemas, and returning `AppDataStores`. The only place that may touch pool creation for app data.
+_Avoid_: Repository::open as the global DB entry (once migrated), sqlite_pool export