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).
Christian Nennemann
c256c38ffb