enable short backtraces by default

Uses panic_backtrace_config feature to set BacktraceStyle::Short,
so panics show useful backtraces without needing RUST_BACKTRACE=1.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/bin/consciousness.rs

@@ -1,2 +1,7 @@
+#![feature(panic_backtrace_config)]
 #![warn(unreachable_pub)]
-fn main() { consciousness::user::main() }
+
+fn main() {
+    std::panic::set_backtrace_style(std::panic::BacktraceStyle::Short);
+    consciousness::user::main()
+}

src/main.rs

@@ -1,3 +1,5 @@
+#![feature(panic_backtrace_config)]
+
 // poc-memory: graph-structured memory for AI assistants
 //
 // Authors: ProofOfConcept <poc@bcachefs.org> and Kent Overstreet
@@ -617,6 +619,8 @@ impl Run for AdminCmd {
 }
 
 fn main() {
+    std::panic::set_backtrace_style(std::panic::BacktraceStyle::Short);
+
     // Handle --help ourselves for expanded subcommand display
     let args: Vec<String> = std::env::args().collect();
     if args.len() <= 1 || args.iter().any(|a| a == "--help" || a == "-h") && args.len() == 2 {