docs: add batch-capable nip-07 extension proposal

Forward-looking design note for a hypothetical "bitvid nip-07" signer
extension that removes the serialized-extension decryption ceiling
(the DM/watch-history/hashtag see-saw) via a batch decrypt/encrypt API,
an internal worker pool, and conversation-key caching — without
exposing the user's private key. Covers the root-cause analysis grounded
in the current queue/priority code, the proposed namespaced surface,
client adoption with graceful fallback, the security model (incl. the
opt-in getConversationKey tradeoff), and the app classes it unlocks.

Indexed under docs/README.md → Nostr Protocol.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

docs/README.md

@@ -15,6 +15,7 @@ Welcome to the bitvid documentation. This directory contains detailed architectu
 - **[Nostr Event Schemas](./nostr-event-schemas.md)**: The definitive catalogue of all Nostr event kinds and data structures used by bitvid.
 - **[DM Privacy Model](./dm-privacy-model.md)**: How Direct Messages are handled, including NIP-17 relays and privacy controls.
 - **[NIP-46 Client Overview](./nip46-client-overview.md)**: Details on the NIP-46 remote signer implementation.
+- **[Batch-Capable nip-07 Extension Proposal](./bitvid-nip07-extension-proposal.md)**: Exploratory design for a signer extension that parallelizes bulk decryption (DMs, watch history) without exposing keys.
 
 ## Moderation & Safety