build: Add clap_complete, libc dependencies and git hash build script

Add clap_complete for shell completion generation and libc (unix-only)
for SIGPIPE handling. Create build.rs to embed the git commit hash at
compile time via cargo:rustc-env=GIT_HASH, enabling `lore version` to
display the short hash alongside the version number.

Co-Authored-By: Claude (us.anthropic.claude-opus-4-5-20251101-v1:0) <noreply@anthropic.com>

build.rs

@@ -0,0 +1,10 @@
+fn main() {
+    let hash = std::process::Command::new("git")
+        .args(["rev-parse", "--short", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .unwrap_or_default();
+    println!("cargo:rustc-env=GIT_HASH={}", hash.trim());
+    println!("cargo:rerun-if-changed=.git/HEAD");
+}