XeWeCore 3.1.1

XeWeCore is the modular firmware core for ESP32, as one Arduino library: a serial console, a
"$group command" command line, typed NVS storage, small helpers and a module framework. Use it on
its own from the Arduino IDE, or through an xewe-os project (github.com/xewe-labs/xewe-os), whose
tools pull it in together with the ready-made modules.

3.1.1 follows 3.1.0 and corrects the sections of src/XeWeCore/Config.h. No behaviour changes.

FIXED

- The serial baud rate, TX and RX buffer sizes, startup delay, echo switch and the banner switch
  are compile-time constants, not runtime defaults: the core has no settings table, and these
  values fill SerialPortConfig and OsConfig once at begin. They moved to the compile-time section
  of Config.h; names and values are unchanged.
- doc/config.md describes the project's Config.h as a catalogue: every generated entry is a
  comment line and its definition commented out, nothing is active until a line is uncommented,
  and an uncommented line is a bare #define. Projects get that form from xewe-os-tools 3.1.3.

INSTALL

- Arduino IDE: Library Manager, XeWeCore 3.1.1. Depends on ArduinoJson >=7.0.0 (tested 7.4.3).
- xewe-os projects: [core] ref = "3.1.1" in xewe.toml, then ./setup.sh. Built and tested with
  xewe-os-tools 3.1.2, arduino-cli 1.5.1 and esp32 core 3.3.12.

TESTING

What was tested, on which tree and with which result: release_card.md, generated by
scripts/release.sh --prepare 3.1.1 and attached to this release. Host tests: 100 (c++17) and
125 (gnu++2b). Board tests ran on an ESP32-C3; the C6 and S3 images were compiled, not run.
