docs: add crate-level documentation and public API doc comments

- Expand crate-level docs for quicprochat-rpc (architecture, wire format,
  module map) and quicprochat-sdk (connection lifecycle, event subscription,
  module descriptions).
- Add /// doc comments to all undocumented pub fn/struct/enum items in
  server domain services (keys, channels, devices, users, account, p2p,
  blobs) and domain types.
- Fix rustdoc broken intra-doc links in plugin-api (HookResult,
  qpc_plugin_init), federation/mod.rs (Store), and client main.rs
  (unescaped brackets).

crates/quicprochat-rpc/src/lib.rs

@@ -1,9 +1,43 @@
 //! QUIC RPC framework for quicprochat v2.
 //!
-//! Wire format per QUIC stream:
-//! - Request:  `[method_id: u16][request_id: u32][payload_len: u32][protobuf bytes]`
-//! - Response: `[status: u8][request_id: u32][payload_len: u32][protobuf bytes]`
-//! - Push:     `[event_type: u16][payload_len: u32][protobuf bytes]` (uni-stream)
+//! This crate implements a lightweight, binary-framed RPC protocol over QUIC.
+//! Each RPC call opens a new QUIC bi-directional stream, sends a request frame,
+//! and reads a response frame. Server-initiated push events use uni-streams.
+//!
+//! # Wire format
+//!
+//! All integers are big-endian.
+//!
+//! **Request** (client → server, bi-stream):
+//! ```text
+//! [method_id: u16][request_id: u32][payload_len: u32][protobuf bytes]
+//! ```
+//!
+//! **Response** (server → client, same bi-stream):
+//! ```text
+//! [status: u8][request_id: u32][payload_len: u32][protobuf bytes]
+//! ```
+//!
+//! **Push** (server → client, uni-stream):
+//! ```text
+//! [event_type: u16][payload_len: u32][protobuf bytes]
+//! ```
+//!
+//! # Architecture
+//!
+//! - [`framing`] — frame types ([`framing::RequestFrame`], [`framing::ResponseFrame`],
+//!   [`framing::PushFrame`]) and encode/decode logic.
+//! - [`method`] — [`method::MethodRegistry`] maps `u16` method IDs to async handler
+//!   functions with optional per-method timeouts.
+//! - [`server`] — [`server::RpcServer`] binds a QUIC endpoint, performs an auth
+//!   handshake on each connection, then dispatches RPC streams to registered handlers.
+//! - [`client`] — [`client::RpcClient`] connects to the server with TLS, supports
+//!   auto-reconnect with exponential backoff, and multiplexes concurrent RPCs.
+//! - [`push`] — [`push::PushBroker`] manages per-identity push connections and
+//!   fan-out to channel members.
+//! - [`middleware`] — session validation, rate limiting, and structured audit logging.
+//! - [`auth_handshake`] — initial session-token exchange on the first bi-stream.
+//! - [`error`] — [`error::RpcError`] and [`error::RpcStatus`] types.
 
 pub mod auth_handshake;
 pub mod framing;