fix(docs): correct Flutter version, add Rust 1.71.0, fix Ubuntu 24.04 meson install, add rsync

- Flutter: 3.38.5 → 3.38.1 (all platforms; confirmed by libflutter.so identity match
  during reproducible build verification)
- Rust: add 1.71.0 to all rustup install lines; required by
  crypto_plugins/frostdart/scripts/linux/build_all.sh which hardcodes cargo +1.71.0
- Ubuntu 24.04 meson: replace pipx with python3-venv approach; pipx cannot install
  library-only packages (markupsafe, jinja2, etc.) and will fail; setuptools added
  because Python 3.12 removed distutils which meson needs for GObject introspection
- Linux desktop deps: add rsync; required by
  crypto_plugins/flutter_libmwc/scripts/linux/build_all.sh

Fixes found during WalletScrutiny reproducible build verification (issue #1399).

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

Author: xrviv

docs/building.md

@@ -14,7 +14,7 @@ Here you will find instructions on how to install the necessary tools for buildi
 The following instructions are for building and running on a Linux host.  Alternatively, see the [Mac](#mac-host) and/or [Windows](#windows-host) section.  This entire section (except for the Android Studio section) needs to be completed in WSL if building on a Windows host.
 
 ### Flutter
-Install Flutter 3.38.5 by [following their guide](https://docs.flutter.dev/get-started/install/linux/desktop?tab=download#install-the-flutter-sdk).  Run `flutter doctor` in a terminal to confirm its installation.
+Install Flutter 3.38.1 by [following their guide](https://docs.flutter.dev/get-started/install/linux/desktop?tab=download#install-the-flutter-sdk).  Run `flutter doctor` in a terminal to confirm its installation.
 
 ### Android Studio
 Install Android Studio.  Follow instructions here [https://developer.android.com/studio/install#linux](https://developer.android.com/studio/install#linux) or install via snap:
@@ -54,15 +54,18 @@ pip3 install --upgrade meson==0.64.1 markdown==3.4.1 markupsafe==2.1.1 jinja2==3
 
 For Ubuntu 24.04,
 ```
-sudo apt install pipx libgcrypt20-dev libglib2.0-dev libsecret-1-dev
-pipx install meson==0.64.1 markdown==3.4.1 markupsafe==2.1.1 jinja2==3.1.2 pygments==2.13.0 toml==0.10.2 typogrify==2.0.7 tomli==2.0.1
+sudo apt install python3-pip python3-venv libgcrypt20-dev libglib2.0-dev libsecret-1-dev
+python3 -m venv ~/.build-tools
+~/.build-tools/bin/pip install meson==0.64.1 markdown==3.4.1 markupsafe==2.1.1 jinja2==3.1.2 pygments==2.13.0 toml==0.10.2 typogrify==2.0.7 tomli==2.0.1 setuptools
+echo 'export PATH="$HOME/.build-tools/bin:$PATH"' >> ~/.bashrc && source ~/.bashrc
 ```
+Note: `pipx` cannot install library-only packages (e.g. `markupsafe`, `jinja2`) and will fail.  `setuptools` is required because Python 3.12 removed `distutils`, which meson needs for GObject introspection.
 
 Install [Rust](https://www.rust-lang.org/tools/install) via [rustup.rs](https://rustup.rs), the required Rust toolchains, and `cargo-ndk` with command:
 ```
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
 source ~/.bashrc
-rustup install 1.89.0 1.85.1 1.81.0
+rustup install 1.89.0 1.85.1 1.81.0 1.71.0
 rustup default 1.89.0
 cargo install cargo-ndk
 ```
@@ -75,12 +78,12 @@ rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-andro
 
 Linux desktop specific dependencies:
 ```
-sudo apt-get install clang cmake ninja-build pkg-config libgtk-3-dev liblzma-dev meson python3-pip libgirepository1.0-dev valac xsltproc docbook-xsl
-pip3 install --upgrade meson==0.64.1 markdown==3.4.1 markupsafe==2.1.1 jinja2==3.1.2 pygments==2.13.0 toml==0.10.2 typogrify==2.0.7 tomli==2.0.1
+sudo apt-get install clang cmake ninja-build pkg-config libgtk-3-dev liblzma-dev meson python3-pip libgirepository1.0-dev valac xsltproc docbook-xsl rsync
 ```
+Note: `rsync` is required by `crypto_plugins/flutter_libmwc/scripts/linux/build_all.sh`.
 
 ### Flutter
-Install Flutter 3.38.5 by [following their guide](https://docs.flutter.dev/install/manual).
+Install Flutter 3.38.1 by [following their guide](https://docs.flutter.dev/install/manual).
 
 Run `flutter doctor` in a terminal to confirm its installation.
 
@@ -213,7 +216,7 @@ Download and install [Rust](https://www.rust-lang.org/tools/install).  [Rustup](
 ```
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
 source ~/.bashrc 
-rustup install 1.89.0 1.85.1 1.81.0
+rustup install 1.89.0 1.85.1 1.81.0 1.71.0
 rustup default 1.89.0
 cargo install cargo-ndk
 cargo install cbindgen cargo-lipo
@@ -223,7 +226,7 @@ rustup target add aarch64-apple-ios aarch64-apple-darwin
 Optionally download [Android Studio](https://developer.android.com/studio) as an IDE and activate its Dart and Flutter plugins.  VS Code may work as an alternative, but this is not recommended.
 
 ### Flutter
-Install 3.38.5 on your Mac host by [following their guide](https://docs.flutter.dev/install/manual).  Run `flutter doctor` in a terminal to confirm its installation.
+Install Flutter 3.38.1 on your Mac host by [following their guide](https://docs.flutter.dev/install/manual).  Run `flutter doctor` in a terminal to confirm its installation.
 
 ### Build plugins and configure
 #### Building plugins for iOS 
@@ -289,12 +292,12 @@ If the DLLs were built on the WSL filesystem instead of on Windows, copy the res
 Frostdart will be built by the Windows host later.
 
 ### Install Flutter on Windows host
-Install Flutter 3.38.5 on your Windows host (not in WSL2) by [following their guide](https://docs.flutter.dev/install/manual).  Run `flutter doctor` in PowerShell to confirm its installation.
+Install Flutter 3.38.1 on your Windows host (not in WSL2) by [following their guide](https://docs.flutter.dev/install/manual).  Run `flutter doctor` in PowerShell to confirm its installation.
 
 ### Rust
 Install [Rust](https://www.rust-lang.org/tools/install) on the Windows host (not in WSL2).  Download the installer from [rustup.rs](https://rustup.rs), make sure it works on the commandline (you may need to open a new terminal), and install the following versions:
 ```
-rustup install 1.89.0 1.85.1 1.81.0
+rustup install 1.89.0 1.85.1 1.81.0 1.71.0
 rustup default 1.89.0
 cargo install cargo-ndk
 ```