fix: thread slug + resolved_env from prepare to each backend's _resolve_plan

BottleBackend.prepare computed slug and resolved_env but never passed
them to _resolve_plan. The concrete docker/smolmachines _resolve_plan
methods still had the old (spec, *, stage_dir) signature too, so
prepare's kwargs blew up with "unexpected keyword argument
'instance_name'" the moment cli.py start was invoked.

Update the abstract _resolve_plan signature and both backend
implementations to accept the full kwarg set prepare passes, and
forward to resolve_plan.resolve_plan() with everything.

bot_bottle/backend/smolmachines/backend.py

@@ -42,9 +42,35 @@ class SmolmachinesBottleBackend(
         return _smolvm.is_available()
 
     def _resolve_plan(
-        self, spec: BottleSpec, *, stage_dir: Path
+        self,
+        spec: BottleSpec,
+        *,
+        slug: str,
+        resolved_env,
+        instance_name: str,
+        agent_image: str,
+        prompt_file: Path,
+        agent_provision_plan,
+        agent_dockerfile_path: str,
+        egress_plan,
+        git_gate_plan,
+        supervise_plan,
+        stage_dir: Path,
     ) -> SmolmachinesBottlePlan:
-        return _resolve_plan.resolve_plan(spec, stage_dir=stage_dir)
+        return _resolve_plan.resolve_plan(
+            spec,
+            slug=slug,
+            resolved_env=resolved_env,
+            instance_name=instance_name,
+            agent_image=agent_image,
+            agent_dockerfile_path=agent_dockerfile_path,
+            prompt_file=prompt_file,
+            agent_provision_plan=agent_provision_plan,
+            egress_plan=egress_plan,
+            supervise_plan=supervise_plan,
+            git_gate_plan=git_gate_plan,
+            stage_dir=stage_dir,
+        )
 
     @contextmanager
     def launch(