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.

compose.yaml

@@ -29,6 +29,7 @@ services:
       CLOUD_PUBLIC_CREDENTIALS_JSON: ${CLOUD_PUBLIC_CREDENTIALS_JSON}
       CLOUD_HOST_CREDENTIALS_JSON: ${CLOUD_HOST_CREDENTIALS_JSON}
       CLOUD_ENROLLMENT_TOKENS_JSON: ${CLOUD_ENROLLMENT_TOKENS_JSON:-[]}
+      CLOUD_SELF_SERVICE_ENROLLMENT_ENABLED: ${CLOUD_SELF_SERVICE_ENROLLMENT_ENABLED:-false}
       CLOUD_SCHEDULER_INTERVAL_SECONDS: ${CLOUD_SCHEDULER_INTERVAL_SECONDS:-1}
       CLOUD_LEASE_REAPER_INTERVAL_SECONDS: ${CLOUD_LEASE_REAPER_INTERVAL_SECONDS:-5}
       CLOUD_LEASE_DURATION_SECONDS: ${CLOUD_LEASE_DURATION_SECONDS:-60}
@@ -53,6 +54,10 @@ services:
       retries: 12
     restart: unless-stopped
 
+  # Before the first `docker compose up`, create the one-time local operator
+  # account interactively: `docker compose run --rm host-agent device-host-agent setup`.
+  # The daemon's default command below has no TTY and fails fast if that
+  # account does not already exist under HOST_AGENT_LOCAL_ACCOUNT_PATH.
   host-agent:
     build:
       context: .
@@ -63,6 +68,7 @@ services:
       HOST_AGENT_TOKEN: ${HOST_AGENT_TOKEN}
       HOST_AGENT_ENROLLMENT_TOKEN: ${HOST_AGENT_ENROLLMENT_TOKEN:-}
       HOST_AGENT_IDENTITY_PATH: ${HOST_AGENT_IDENTITY_PATH:-/app/tasks/host_identity.json}
+      HOST_AGENT_LOCAL_ACCOUNT_PATH: ${HOST_AGENT_LOCAL_ACCOUNT_PATH:-/app/tasks/host_local_account.json}
       HOST_AGENT_DISPLAY_NAME: ${HOST_AGENT_DISPLAY_NAME:-}
       HOST_AGENT_HEARTBEAT_INTERVAL_SECONDS: ${HOST_AGENT_HEARTBEAT_INTERVAL_SECONDS:-30}
       HOST_AGENT_POLL_TIMEOUT_SECONDS: ${HOST_AGENT_POLL_TIMEOUT_SECONDS:-20}