Install an agent on a one-off PC from a single command

An admin generates a short-lived token in Settings > Endpoints > Endpoints and
copies the command it produces. A tech runs that one line in an elevated
PowerShell on a PC with no agent:

    powershell -ExecutionPolicy Bypass -c "irm https://<server>/shopdb/api/
    endpoints/siteagent/bootstrap.ps1?t=<token> | iex"

The script refuses to run unelevated, refuses a PC that already has the agent
(a managed bay gets it from GE-Enforce), downloads the package the existing
builder produces, checks both binaries against the hashes the server baked in,
installs with NO shared key, and reports what happened. The PC then asks to
enroll and waits for an admin to approve it, which the script watches for
locally for two minutes before exiting.

- New endpointbootstraptokens table and migration
  endpoints0024bootstraptokens: hash only, expiry, use count, revoke.
- Admin routes to generate, list and revoke tokens; the secret is shown once.
- Two token-only routes: the script, and the package (which spends a use).
  Anything wrong with the token answers 404 rather than confirming it exists,
  both are rate limited per address and both are audited with the caller.
- The package builder is now shared rather than duplicated, and a bootstrap
  package can never carry a collector key.

plugins/endpoints/models/__init__.py

@@ -9,6 +9,7 @@ from .operatorreport import OperatorReport
 from .credential import (
     EndpointCredential, EndpointEnrollRequest, EndpointMigrationWave,
 )
+from .bootstrap import EndpointBootstrapToken
 from .health import (
     EndpointHealthState, EndpointHealthTransition, EndpointMonitorImpact,
 )
@@ -18,5 +19,6 @@ __all__ = [
     'EndpointLock', 'EndpointLogCollection',
     'EndpointMonitor', 'OperatorReport',
     'EndpointCredential', 'EndpointEnrollRequest', 'EndpointMigrationWave',
+    'EndpointBootstrapToken',
     'EndpointHealthState', 'EndpointHealthTransition', 'EndpointMonitorImpact',
 ]