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>

crates/quicproquo-server/migrations/002_add_seq.sql

@@ -0,0 +1,21 @@
+-- Migration 002: add per-inbox delivery sequence numbers.
+--
+-- Adds a `seq` column to the deliveries table and a separate counter table
+-- that tracks the next sequence number per (recipient_key, channel_id) inbox.
+-- The counter is atomically incremented on each enqueue via an UPSERT so
+-- sequence numbers are gapless even under concurrent inserts.
+--
+-- Requires SQLite >= 3.35 (RETURNING clause support; available on Ubuntu 22.04+).
+
+ALTER TABLE deliveries ADD COLUMN seq INTEGER NOT NULL DEFAULT 0;
+
+CREATE TABLE IF NOT EXISTS delivery_seq_counters (
+    recipient_key BLOB    NOT NULL,
+    channel_id    BLOB    NOT NULL,
+    next_seq      INTEGER NOT NULL DEFAULT 0,
+    PRIMARY KEY (recipient_key, channel_id)
+);
+
+-- Index lets ORDER BY seq queries use an index scan instead of a sort.
+CREATE INDEX IF NOT EXISTS idx_del_seq
+    ON deliveries (recipient_key, channel_id, seq);