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.

.vscode/launch.json

@@ -2,10 +2,10 @@
   "version": "0.2.0",
   "configurations": [
     {
-      "name": "Launch BTerminal (v1)",
+      "name": "Launch Agents Orchestrator (v1)",
       "type": "debugpy",
       "request": "launch",
-      "program": "${workspaceFolder}/bterminal.py"
+      "program": "${workspaceFolder}/# v1 removed"
     }
   ]
 }