refactor(agent): use agent-neutral runtime names

Assisted-by: Codex

docs/prds/0023-smolmachines-backend.md

@@ -317,7 +317,7 @@ The feature is **done** when all of the following ship:
 bot_bottle/backend/smolmachines/
   __init__.py            re-exports SmolmachinesBottleBackend
   backend.py             SmolmachinesBottleBackend façade
-  bottle.py              SmolmachinesBottle (exec_claude / exec / cp_in / close)
+  bottle.py              SmolmachinesBottle (exec_agent / exec / cp_in / close)
   bottle_plan.py         SmolmachinesBottlePlan + .print()
   bottle_cleanup_plan.py SmolmachinesBottleCleanupPlan
   prepare.py             resolve_plan(spec, stage_dir, ...) -> SmolmachinesBottlePlan
@@ -436,7 +436,7 @@ Three changes vs. the Docker backend:
    layer enforces it.
 3. Provisioning: CA install → prompt → skills → git → supervise
    config, each via `smolvm machine exec` / `smolvm machine cp`.
-4. Yield a `SmolmachinesBottle` whose `exec_claude` / `exec` /
+4. Yield a `SmolmachinesBottle` whose `exec_agent` / `exec` /
    `cp_in` all funnel through `smolvm machine exec` /
    `smolvm machine cp`.
 5. Teardown: stop and delete the VM → stop + remove the bundle