refactor(backend): pass Bottle to provisioners instead of target string

Closes #178.

The backend provision functions now receive a Bottle handle with
exec / cp_in methods instead of a raw target string. Provisioner
modules use bottle.exec and bottle.cp_in in place of inlined
subprocess.run(["docker", "exec"/"cp", ...]) and direct
_smolvm.machine_cp / machine_exec calls. This decouples the
provisioners from backend-specific runtime primitives so future
refactors (e.g. the supervise rework) can swap the bottle's exec
implementation without touching every provisioner.

Each launch.py constructs the Bottle handle before calling
provision so it can be passed in; provision_prompt's return value
is wired back onto the bottle's prompt path attribute after the
fact.

bot_bottle/backend/__init__.py

@@ -312,15 +312,13 @@ class BottleBackend(ABC, Generic[PlanT, CleanupT]):
     def launch(self, plan: PlanT) -> AbstractContextManager[Bottle]:
         """Build/run the bottle and yield a handle; tear down on exit."""
 
-    def provision(self, plan: PlanT, target: str) -> str | None:
+    def provision(self, plan: PlanT, bottle: "Bottle") -> str | None:
         """Copy host-side files (CA cert, prompt, skills, .git) into
         the running bottle. Called from `launch` after the container
-        / machine is up. `target` identifies the running instance in
-        backend-specific terms (Docker: resolved container name; fly:
-        machine id). Returns the in-container prompt path if a prompt
-        was provisioned, else None — the Bottle handle uses it to
-        decide whether to add provider-specific prompt args to the agent's
-        argv.
+        / machine is up. Returns the in-container prompt path if a
+        prompt was provisioned, else None — the Bottle handle uses it
+        to decide whether to add provider-specific prompt args to the
+        agent's argv.
 
         Default orchestration: ca → prompt → skills → workspace → git →
         supervise. CA install runs first so the agent's trust store
@@ -333,16 +331,16 @@ class BottleBackend(ABC, Generic[PlanT, CleanupT]):
         on the agent's HTTP_PROXY path so every tool that respects
         HTTPS_PROXY (claude-code, git over HTTPS, npm, curl) is
         intercepted without per-tool reconfiguration."""
-        self.provision_ca(plan, target)
-        prompt_path = self.provision_prompt(plan, target)
-        self.provision_provider_auth(plan, target)
-        self.provision_skills(plan, target)
-        self.provision_workspace(plan, target)
-        self.provision_git(plan, target)
-        self.provision_supervise(plan, target)
+        self.provision_ca(plan, bottle)
+        prompt_path = self.provision_prompt(plan, bottle)
+        self.provision_provider_auth(plan, bottle)
+        self.provision_skills(plan, bottle)
+        self.provision_workspace(plan, bottle)
+        self.provision_git(plan, bottle)
+        self.provision_supervise(plan, bottle)
         return prompt_path
 
-    def provision_ca(self, plan: PlanT, target: str) -> None:
+    def provision_ca(self, plan: PlanT, bottle: "Bottle") -> None:
         """Install the per-bottle CA into the agent's trust store so
         the agent trusts the bumped CONNECT cert egress (was
         pipelock, pre-PRD-0017) presents. Default impl is a no-op so
@@ -351,34 +349,34 @@ class BottleBackend(ABC, Generic[PlanT, CleanupT]):
         backend overrides to docker-cp the cert in and run
         `update-ca-certificates`."""
 
-    def provision_provider_auth(self, plan: PlanT, target: str) -> None:
+    def provision_provider_auth(self, plan: PlanT, bottle: "Bottle") -> None:
         """Install non-secret provider auth marker files into the agent
         home when a provider needs them to select the right auth mode.
         The default is no-op."""
 
     @abstractmethod
-    def provision_prompt(self, plan: PlanT, target: str) -> str | None:
+    def provision_prompt(self, plan: PlanT, bottle: "Bottle") -> str | None:
         """Copy the prompt file into the running bottle. Returns the
         in-container path iff the agent has a non-empty prompt;
         callers use the return value to decide whether to add
         provider-specific prompt args to the agent's argv."""
 
     @abstractmethod
-    def provision_skills(self, plan: PlanT, target: str) -> None:
+    def provision_skills(self, plan: PlanT, bottle: "Bottle") -> None:
         """Copy the agent's named skills from the host into the
         running bottle. No-op when the agent has no skills."""
 
-    def provision_workspace(self, plan: PlanT, target: str) -> None:
+    def provision_workspace(self, plan: PlanT, bottle: "Bottle") -> None:
         """Copy the operator workspace into the running bottle when
         the backend cannot bake it into the agent image. Default is
         no-op for backends like Docker that handle this before launch."""
 
     @abstractmethod
-    def provision_git(self, plan: PlanT, target: str) -> None:
+    def provision_git(self, plan: PlanT, bottle: "Bottle") -> None:
         """Copy the host's cwd `.git` directory into the running
         bottle if the user requested --cwd. No-op otherwise."""
 
-    def provision_supervise(self, plan: PlanT, target: str) -> None:
+    def provision_supervise(self, plan: PlanT, bottle: "Bottle") -> None:
         """Write the in-bottle Claude Code MCP config so the agent
         discovers the per-bottle supervise sidecar (PRD 0013).
         No-op when bottle.supervise is False or the backend doesn't