add Windows support (Phase 1)

Cross-platform paths: config_dir() uses %APPDATA%, data_dir() uses
%PROGRAMDATA% on Windows. TLS cert directory uses data_dir() instead
of hardcoded /usr/local/var/numa. Windows DNS discovery via ipconfig.
Fixed cfg gates from not(macos) to explicit linux to prevent Linux
code compiling on Windows. Added Windows target to CI and release
workflows with zip packaging.

System integration (numa install/service) not yet supported on Windows
— users run numa.exe manually.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/tls.rs

@@ -10,14 +10,11 @@ use time::{Duration, OffsetDateTime};
 const CA_VALIDITY_DAYS: i64 = 3650; // 10 years
 const CERT_VALIDITY_DAYS: i64 = 365; // 1 year
 
-/// TLS certs use a fixed system path — both the daemon and `sudo numa install` must agree.
-pub const TLS_DIR: &str = "/usr/local/var/numa";
-
 /// Build a TLS config with a cert covering all provided service names.
 /// Wildcards under single-label TLDs (*.numa) are rejected by browsers,
 /// so we list each service explicitly as a SAN.
 pub fn build_tls_config(tld: &str, service_names: &[String]) -> crate::Result<Arc<ServerConfig>> {
-    let dir = std::path::PathBuf::from(TLS_DIR);
+    let dir = crate::data_dir();
     let (ca_cert, ca_key) = ensure_ca(&dir)?;
     let (cert_chain, key) = generate_service_cert(&ca_cert, &ca_key, tld, service_names)?;