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/bttask.rs

@@ -19,7 +19,7 @@ fn db_path() -> PathBuf {
     DB_PATH.get().cloned().unwrap_or_else(|| {
         dirs::data_dir()
             .unwrap_or_else(|| PathBuf::from("."))
-            .join("bterminal")
+            .join("agor")
             .join("btmsg.db")
     })
 }