refactor: use Cargo workspace

Cargo.toml

@@ -0,0 +1,22 @@
+[workspace]
+resolver = "3"
+members = [
+    "cli",
+    "packages/core",
+    "packages/localsend_isolates/rust",
+    "server",
+]
+
+# Profiles are only honored in the workspace root manifest.
+
+# Full debuginfo dominates target/ size; line tables keep backtraces usable.
+[profile.dev]
+debug = "line-tables-only"
+
+# RSA key generation is bignum-heavy and takes ~10x longer unoptimized;
+# keep the crypto crates optimized in dev so tests stay fast.
+[profile.dev.package.rsa]
+opt-level = 2
+
+[profile.dev.package.num-bigint-dig]
+opt-level = 2