feat: versioning SemVer MAJOR.MINOR.PATCH basé sur git describe

- backend/version.py: get_version() lit git describe --tags (ex: 1.8.0-301-gabc1234)
- main.py: FastAPI version = get_version() dynamique
- build.rs: injecte GIT_VERSION, GIT_HASH, SEMVER depuis git describe
- main.rs: ABOUT_MSG, get_version(), log utilisent GIT_VERSION
- Format: MAJOR.MINOR.PATCH[-commits-gHASH] (ex: 1.8.0, 1.8.0-3-gabc1234)
- Fallback: VERSION file ou 0.0.0-dev si Git indisponible

desktop/build.rs

@@ -1,6 +1,15 @@
 fn main() {
-    // Inject Git commit hash as version suffix
-    let git_hash = std::process::Command::new("git")
+    // Get version from git describe (same as backend/version.py)
+    let version = std::process::Command::new("git")
+        .args(["describe", "--tags", "--dirty=-dirty"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().trim_start_matches('v').to_string())
+        .unwrap_or_else(|| "0.0.0-dev".to_string());
+
+    // Extract short hash for display
+    let short_hash = std::process::Command::new("git")
         .args(["rev-parse", "--short", "HEAD"])
         .output()
         .ok()
@@ -8,9 +17,15 @@ fn main() {
         .map(|s| s.trim().to_string())
         .unwrap_or_else(|| "unknown".to_string());
 
-    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
+    // SemVer base (strip -suffix)
+    let semver_base = version.split('-').next().unwrap_or("0.0.0");
+
+    println!("cargo:rustc-env=GIT_VERSION={}", version);
+    println!("cargo:rustc-env=GIT_HASH={}", short_hash);
+    println!("cargo:rustc-env=SEMVER={}", semver_base);
     println!("cargo:rerun-if-changed=.git/HEAD");
     println!("cargo:rerun-if-changed=.git/refs/heads/main");
+    println!("cargo:rerun-if-changed=.git/refs/tags");
 
     tauri_build::build()
 }