Extract data_server into external data-server crate

The data_server module had no dependency on the rest of myc (only
chrono/regex/zip), so it was moved verbatim into a standalone leaf
crate at its own Gitea repo and is now consumed as a git dependency.
A 'pub use ::data_server;' re-export in src/ast/mod.rs keeps all
existing myc::ast::data_server::… paths valid; no call sites changed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -15,6 +15,7 @@ rmcp = { version = "1.2", features = ["server", "transport-io"] }
 tokio = { version = "1", features = ["rt", "io-std", "macros"] }
 serde = { version = "1", features = ["derive"] }
 zip = "2"
+data-server = { git = "http://192.168.178.103:3000/Brummel/data-server.git", branch = "main" }
 
 [dev-dependencies]
 insta = { version = "1.39", features = ["yaml"] }