Fix TUI startup and test script bugs

- TUI: replace per-call bufio.Scanner with a goroutine+channel reader
  (lineReader) so a single scanner lives for the connection lifetime;
  previous pattern silently dropped messages due to scanner read-ahead
- test-tui.sh / test-network.sh: add `return 0` to wait_port — when the
  port opens and the while condition becomes false, bash returned the
  condition's exit code (1) to the caller, tripping set -e immediately
- .gitignore: use /tui (root-only) instead of tui to avoid ignoring cmd/tui/

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

test-network.sh

@@ -23,7 +23,7 @@ CHARLIE_IPC=19343
 NETWORK_NAME="test-$(date +%s)"
 DATA_ROOT="/tmp/waste-test"
 rm -rf "$DATA_ROOT"
-mkdir -p "$DATA_ROOT"
+mkdir -p "$DATA_ROOT/bin"
 
 # ── cleanup ───────────────────────────────────────────────────────────────────
 PIDS=()
@@ -157,6 +157,7 @@ wait_port() {
             exit 1
         fi
     done
+    return 0
 }
 
 # ── build ─────────────────────────────────────────────────────────────────────