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/docker/prepare.py

@@ -63,7 +63,7 @@ def resolve_plan(
     bottle = manifest.bottle_for(spec.agent_name)
     provider = bottle.agent_provider
     provider_runtime = runtime_for(provider.template)
-    guest_home = os.environ.get("BOT_BOTTLE_CONTAINER_HOME", "/home/node")
+    guest_home = "/home/node"
     workspace_plan = resolve_workspace_plan(spec, guest_home=guest_home)
 
     # PRD 0016 follow-up: identity, not bare slug. A fresh `start`