ci: add test pipeline and bump version to 0.2.1

Adds a Drone CI pipeline that runs on push and pull_request events,
executing cargo fmt --check, cargo clippy, and cargo test in sequence.

.drone.yml

@@ -1,5 +1,23 @@
 kind: pipeline
 type: docker
+name: ci
+
+trigger:
+  event:
+    - push
+    - pull_request
+
+steps:
+  - name: test
+    image: rust:latest
+    commands:
+      - cargo fmt --check
+      - cargo clippy -- -D warnings
+      - cargo test
+
+---
+kind: pipeline
+type: docker
 name: release
 
 trigger:

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tmuxido"
-version = "0.2.0"
+version = "0.2.1"
 edition = "2024"
 
 [dev-dependencies]