chore: update tooling (mise, justfile, examples)

Add mise.toml for tool version management, rename Justfile to justfile,
add examples/justfile for running Python examples, and update docs.

justfile

@@ -0,0 +1,29 @@
+set shell := ["bash", "-c"]
+
+# Receive LoRa packets (Ctrl-C to stop)
+rx *args:
+    @mise install && uv run {{source_directory()}}/simple_rx.py {{args}}
+
+# Transmit a single packet
+tx *args:
+    @mise install && uv run {{source_directory()}}/simple_tx.py {{args}}
+
+# Two-dongle ping-pong demo (--role tx|rx)
+ping-pong *args:
+    @mise install && uv run {{source_directory()}}/ping_pong.py {{args}}
+
+# Exercise all DongLoRa commands
+test-commands *args:
+    @mise install && uv run {{source_directory()}}/all_commands.py {{args}}
+
+# Two-way LoRa bridge over TCP
+bridge *args:
+    @mise install && uv run {{source_directory()}}/lora_bridge.py {{args}}
+
+# MeshCore packet decoder/monitor
+meshcore *args:
+    @mise install && uv run {{source_directory()}}/meshcore/meshcore_rx.py {{args}}
+
+# Run any example by name (e.g. just ex run simple_rx)
+run script *args:
+    @mise install && uv run {{source_directory()}}/{{script}}.py {{args}}