Add initial project structure with Rust Nix flake template

- Create .envrc for Direnv configuration
- Add .pre-commit-config.yaml for pre-commit hooks
- Include CONTRIBUTING.md for contribution guidelines
- Initialize Cargo.toml for Rust package configuration
- Update LICENSE to link to full license text
- Create Makefile for build, run, test, and clean commands
- Revise README.md for project description and usage instructions
- Implement default Nix flake configuration in flake.nix
- Add Flatpak manifest for packaging
- Set up project metadata in project.toml
- Create shell.nix for legacy shell support
- Add skeletal Rust application in src/main.rs
- Include sample test in tests/sample_test.rs

flatpak/app.flatpak.json

@@ -0,0 +1,22 @@
+{
+    "app-id": "org.example.rustdevshell",
+    "runtime": "org.freedesktop.Platform",
+    "runtime-version": "23.08",
+    "sdk": "org.freedesktop.Sdk",
+    "command": "rustdevshell-app",
+    "modules": [
+        {
+            "name": "rustdevshell-app",
+            "buildsystem": "simple",
+            "build-commands": [
+                "cargo build --release"
+            ],
+            "sources": [
+                {
+                    "type": "dir",
+                    "path": "../src"
+                }
+            ]
+        }
+    ]
+}