clean(mcp): extract constants, use CARGO_PKG_VERSION, fix unreachable

- extract DEFAULT_DATABASE_URL, DEFAULT_SEARCH_LIMIT, SERVER_NAME
- use env!("CARGO_PKG_VERSION") instead of hardcoded "0.1.0"
- content_type_to_str returns &'static str instead of allocating String
- cfg guard on unreachable pattern in wire_repositories

crates/mcp/src/server.rs

@@ -16,6 +16,8 @@ use uuid::Uuid;
 
 use crate::tools::{channels, library, schedule};
 
+const SERVER_NAME: &str = "k-tv-mcp";
+
 #[derive(Clone)]
 pub struct KTvMcpServer {
     pub channel_cmd_deps: Arc<ChannelCommandDeps>,
@@ -191,8 +193,8 @@ impl ServerHandler for KTvMcpServer {
             protocol_version: ProtocolVersion::V_2024_11_05,
             capabilities: ServerCapabilities::builder().enable_tools().build(),
             server_info: Implementation {
-                name: "k-tv-mcp".into(),
-                version: "0.1.0".into(),
+                name: SERVER_NAME.into(),
+                version: env!("CARGO_PKG_VERSION").into(),
             },
             instructions: Some(
                 "K-TV MCP server. Create channels, define programming blocks, generate schedules. \