Protocol v2: trusted-peer push, truthful partials, split downloads

Three capabilities the iroh-blobs 0.103 line makes possible:

- Push (new API surface, protocol v2): `Push { hash, node_id }` hands
  fully-present content to a trusted peer, unprompted. Consent is
  mutual — the sender pushes only to peers it trusts, and the receiver
  (which now accepts connections unconditionally and gates per request)
  admits pushes only from peers *it* trusts, deferring with RateLimited
  while metered. An accepted push is pinned by the receiver (default
  policy, format inferred from the request ranges) once its transfer
  completes, and surfaces as a PushReceived event. Because QUIC writes
  are fire-and-forget, the sender confirms delivery by observing the
  receiver's bitfields (root + last hashseq child) before replying —
  Pushed { bytes } means verified received, not merely sent. New
  varde-ctl `push` command.

- Truthful partial presence: Status/List report bytes actually present
  and verified for partial blobs, from the store's bitfields via
  observe, instead of the old "0 until complete".

- Split downloads: multi-provider fetches stripe one request across
  providers (SplitStrategy::Split) instead of trying them serially.

Trusted peers may observe bitfields even when serving is disabled or
metered — bitfields are metadata, and push confirmation rides on them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

varde-ctl/src/main.rs

@@ -73,6 +73,14 @@ enum Command {
     /// Peer trust operations
     #[command(subcommand)]
     Peer(PeerCommand),
+    /// Push fully-present content to a trusted peer
+    Push {
+        /// BLAKE3 hash (hex)
+        hash: String,
+        /// The receiving peer's iroh NodeId (z-base-32); must be trusted
+        /// on both sides
+        node_id: String,
+    },
     /// Drop all unpinned blobs
     Gc,
     /// Stream daemon events to stdout (one JSON object per line)
@@ -180,6 +188,7 @@ fn to_request(command: Command) -> Result<Request> {
         Command::Peer(PeerCommand::Trust { node_id }) => Request::PeerTrust { node_id },
         Command::Peer(PeerCommand::Untrust { node_id }) => Request::PeerUntrust { node_id },
         Command::Peer(PeerCommand::List) => Request::PeerList {},
+        Command::Push { hash, node_id } => Request::Push { hash, node_id },
         Command::Gc => Request::Gc {},
         Command::Subscribe => Request::Subscribe {},
     })
@@ -291,5 +300,8 @@ fn print_human(data: Option<&ResponseData>) {
         ResponseData::GcDone { blobs_removed } => {
             println!("gc: removed {blobs_removed} blobs");
         }
+        ResponseData::Pushed { hash, bytes } => {
+            println!("pushed {hash} ({bytes} bytes)");
+        }
     }
 }