chore: fix remaining Antigravity Proxy refs, add systemd unit

- Rename CA org to ZeroGravity
- Fix lib.rs docstring
- Fix mitm-redirect.sh comment
- Fix README title

src/lib.rs

@@ -1,3 +1,3 @@
-//! Antigravity proxy library — shared modules for main proxy and tools.
+//! ZeroGravity library — shared modules for main proxy and tools.
 
 pub mod snapshot;

src/mitm/ca.rs

@@ -115,7 +115,7 @@ impl MitmCa {
 
         let mut dn = DistinguishedName::new();
         dn.push(DnType::CommonName, "Antigravity MITM CA");
-        dn.push(DnType::OrganizationName, "Antigravity Proxy");
+        dn.push(DnType::OrganizationName, "ZeroGravity");
         params.distinguished_name = dn;
 
         params.is_ca = IsCa::Ca(BasicConstraints::Unconstrained);