Implement edge-host-self-enrollment

Host Agent:
- One-time local operator account bootstrap (PBKDF2-HMAC-SHA256, atomic
  0600-permission write) gating the daemon's first unattended start via a
  new `setup` CLI subcommand.
- Default control-plane URL now https://amcp.home.jerryyan.top (env var
  override unchanged).
- Enrollment no longer requires a pre-issued token; falls back to
  zero-token self-service enrollment when none is configured.

Cloud control plane:
- CLOUD_SELF_SERVICE_ENROLLMENT_ENABLED (default false) opt-in flag.
- SelfServiceEnrollmentAuthProvider + ChainedEnrollmentAuthProvider:
  configured tokens still take priority; self-service only applies when
  no token matches, preserving edge-host-enrollment's token-bound path.
- Fixed a latent bug in sql_repository.py::enroll_host: the token-conflict
  lookup used `== enrollment_token_digest`, which SQLAlchemy compiles to
  `IS NULL` when the value is None, so every self-service enrollment after
  the first would have falsely collided with an existing NULL-digest host.
  Skipped that lookup entirely when the digest is None.

Docs/deploy: .env.example, compose.yaml, compose.deploy.yaml,
CLOUD_DEPLOYMENT.md, MACOS_IPHONE_SETUP.md updated for the new flag,
URL default, and required `device-host-agent setup` step.

Verification: 494 non-integration tests pass; openspec validate --strict
passes. PostgreSQL-backed contract tests and full manual end-to-end
verification were not run (no Postgres/Docker or reachable cloud-api in
this environment); noted as unchecked in tasks.md 7.2/7.4.

packages/cloud-platform/cloud/internal_api/api.py

@@ -13,6 +13,7 @@ from fastapi.responses import JSONResponse
 from cloud.auth import (
     AuthProvider,
     ConfiguredEnrollmentTokenProvider,
+    EnrollmentAuthProvider,
     HostAuthorizationError,
     digest_token,
 )
@@ -47,7 +48,7 @@ def create_internal_router(
     *,
     pool: DevicePool,
     auth_provider: AuthProvider,
-    enrollment_auth_provider: ConfiguredEnrollmentTokenProvider | None = None,
+    enrollment_auth_provider: EnrollmentAuthProvider | None = None,
     version_prefix: str = "/internal/v1",
     claim_poll_interval_seconds: float = 0.1,
     lease_duration_seconds: float = 60.0,