Add a `name` field to both `WorkflowDefinition` (optional display name
declared in YAML, e.g. "Continuous Integration") and `WorkflowInstance`
(required, unique alongside the UUID primary key). Instance names are
auto-assigned as `{definition_id}-{N}` via a per-definition monotonic
counter so the 42nd run of `ci` becomes `ci-42`.
Persistence trait gains two methods:
* `get_workflow_instance_by_name` — name-based lookup for Get/Cancel/
Suspend/Resume/Watch/Logs RPCs so callers can address instances
interchangeably as either UUID or human name.
* `next_definition_sequence` — atomic per-definition counter used by
the host at start time to allocate the next N.
This commit wires the in-memory test provider and touches the deno
bridge test helper; the real postgres/sqlite impls follow in the next
commit. UUIDs remain the primary key throughout — names are a second
unique index, never a replacement.
