chore: rename project quicnprotochat -> quicproquo (binaries: qpq)

Rename the entire workspace:
- Crate packages: quicnprotochat-{core,proto,server,client,gui,p2p,mobile} -> quicproquo-*
- Binary names: quicnprotochat -> qpq, quicnprotochat-server -> qpq-server,
  quicnprotochat-gui -> qpq-gui
- Default files: *-state.bin -> qpq-state.bin, *-server.toml -> qpq-server.toml,
  *.db -> qpq.db
- Environment variable prefix: QUICNPROTOCHAT_* -> QPQ_*
- App identifier: chat.quicnproto.gui -> chat.quicproquo.gui
- Proto package: quicnprotochat.bench -> quicproquo.bench
- All documentation, Docker, CI, and script references updated

HKDF domain-separation strings and P2P ALPN remain unchanged for
backward compatibility with existing encrypted state and wire protocol.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/src/contributing/coding-standards.md

@@ -1,6 +1,6 @@
 # Coding Standards
 
-This page defines the engineering standards for quicnprotochat. These are
+This page defines the engineering standards for quicproquo. These are
 non-negotiable -- all code merged into the repository must conform to these
 rules. The standards exist to ensure that every milestone produces
 production-ready, auditable, and secure code.
@@ -86,9 +86,9 @@ pub fn create_group(
 
 - No `unwrap()` or `expect()` on cryptographic operations. All crypto errors
   must be typed and propagated.
-- Use `thiserror` for library error types (`quicnprotochat-core`,
-  `quicnprotochat-proto`) and `anyhow` for application-level error handling
-  (`quicnprotochat-server`, `quicnprotochat-client`).
+- Use `thiserror` for library error types (`quicproquo-core`,
+  `quicproquo-proto`) and `anyhow` for application-level error handling
+  (`quicproquo-server`, `quicproquo-client`).
 - `unwrap()` is acceptable only in:
   - Test code.
   - Cases where the invariant is provably guaranteed by the type system