refactor!: rebrand bterminal to agor (agents-orchestrator)

Rename Cargo crates (bterminal-core→agor-core, bterminal-relay→agor-relay),
env vars (BTERMINAL_*→AGOR_*), config paths (~/.config/agor), CSS custom
properties, plugin API object, package names, and all documentation.

BREAKING CHANGE: config/data paths changed from bterminal to agor.

src-tauri/src/commands/agent.rs

@@ -1,7 +1,7 @@
 use tauri::State;
 use crate::AppState;
 use crate::sidecar::AgentQueryOptions;
-use bterminal_core::sandbox::SandboxConfig;
+use agor_core::sandbox::SandboxConfig;
 
 #[tauri::command]
 #[tracing::instrument(skip(state, options), fields(session_id = %options.session_id))]

src-tauri/src/commands/misc.rs

@@ -31,7 +31,7 @@ pub fn open_url(url: String) -> Result<(), String> {
 
 #[tauri::command]
 pub fn is_test_mode() -> bool {
-    std::env::var("BTERMINAL_TEST").map_or(false, |v| v == "1")
+    std::env::var("AGOR_TEST").map_or(false, |v| v == "1")
 }
 
 #[tauri::command]