feat(agent_provider): migrate tests, drop guest-home/skills-dir env knobs, activate PRD 0050

- tests/unit/test_provision_apply.py covers the new shared
  apply helpers (apply_skills / apply_prompt / apply_provision)
  that replace the per-backend modules deleted in the prior
  commit.
- tests/unit/test_contrib_supervise_mcp.py covers both providers'
  provision_supervise_mcp behavior — confirms the codex bottle
  now runs `codex mcp add` symmetrically with claude.
- tests/unit/test_smolmachines_provision.py drops the four test
  classes whose subjects moved (TestProvisionPrompt /
  TestProvisionProviderAuth / TestProvisionSkills /
  TestProvisionSupervise); the backend-side CA / git / workspace
  classes stay.
- tests/unit/test_docker_provision_provider_auth.py removed; its
  coverage now lives in tests/unit/test_provision_apply.py
  (apply_provision is backend-agnostic, one test file suffices).

Drops the BOT_BOTTLE_CONTAINER_HOME, BOT_BOTTLE_GUEST_HOME,
BOT_BOTTLE_CONTAINER_SKILLS_DIR, and BOT_BOTTLE_GUEST_SKILLS_DIR
env knobs the deleted provision modules used to read. /home/node
is hardcoded everywhere the knobs lived; the values were
effectively constants today and removing them keeps the PRD-0050
surface area honest.

Flips PRD 0050 Status: Draft → Active. Closes #177 on merge.

bot_bottle/backend/smolmachines/provision/git.py

@@ -36,15 +36,12 @@ from ... import Bottle
 from ..bottle_plan import SmolmachinesBottlePlan
 
 
-# `node` is the agent user from the repo Dockerfile. Override via
-# BOT_BOTTLE_GUEST_HOME mirrors the docker backend's
-# BOT_BOTTLE_CONTAINER_HOME knob — same purpose, different
-# transport.
-_DEFAULT_GUEST_HOME = "/home/node"
+# `node` is the agent user from the repo Dockerfile.
+_GUEST_HOME = "/home/node"
 
 
 def _guest_home() -> str:
-    return os.environ.get("BOT_BOTTLE_GUEST_HOME", _DEFAULT_GUEST_HOME)
+    return _GUEST_HOME
 
 
 def provision_git(plan: SmolmachinesBottlePlan, bottle: Bottle) -> None: