Switch orchestrator_config from a generic key/text store to a typed
single-row table with a dedicated teardown_timeout_seconds REAL column.
The CHECK (id = 1) constraint enforces at most one config row.
Remove TEARDOWN_TIMEOUT_KEY constant; update OrchestratorConfigStore to
expose get/set/delete_teardown_timeout_seconds() instead of the generic
get/set/delete(key). Resolving the DB value in resolve_teardown_timeout()
no longer needs a float() conversion since the column is already REAL.
If resolve_teardown_timeout() raised after launch_consolidated()/register_agent()
returned, the teardown callback was never registered, leaving the bottle
registered with no cleanup path. Resolve the timeout into a local variable
before the registration call so any failure aborts before the bottle exists.
Add tests covering OrchestratorConfigStore, resolve_teardown_timeout priority
ordering (env > db > default), and the source-order invariant that the resolver
runs before registration in all three backends.