iam: self-service ops, optional workspace filters, Mux service routing (#855)

Three threads, all reinforcing the contract's system-level vs.
workspace-association distinction.

WS Mux service routing
- tg-show-flows (and any workspace-level service over the WS) was
  failing with "unknown service" because the post-refactor Mux
  unconditionally looked up flow-service:<kind>.  Now branches on
  the envelope's flow field: with flow → flow-service:<kind>;
  without flow → <kind>:<op> from the inner body; with bare op
  lookup for service=iam.  Resource and parameters come from the
  matched op's own extractors — same path the HTTP endpoints take.

Optional workspace on system-level user/key ops
- list-users returns the deployment-wide list when no workspace is
  supplied, filters when one is.  get-user, update-user,
  disable-user, enable-user, delete-user, reset-password,
  create-api-key, list-api-keys, revoke-api-key all treat workspace
  as an optional integrity check rather than a required argument.
- create-user keeps workspace required — there it's the new user's
  home-workspace binding, a parameter rather than an address.
- API keys reclassified as SYSTEM-level resources.  By the same
  reasoning that makes users system-level, an API key is a
  credential record on a deployment-wide registry; the workspace it
  authenticates to is a property, not a containment.

Self-service surface
- whoami: returns the caller's own user record.  AUTHENTICATED-only;
  no users:read capability required.  Foundation for UI affordances
  that depend on the caller's permissions.
- bootstrap-status: POST /api/v1/auth/bootstrap-status, PUBLIC,
  side-effect-free.  Returns {bootstrap_available: bool} so a
  first-run UI can decide whether to render setup without consuming
  the bootstrap op.
- Gateway now injects actor=identity.handle on every authenticated
  forward to iam-svc (IamEndpoint and WS Mux iam path), overwriting
  any caller-supplied value.  Underpins whoami, audit logging, and
  future regime-side decisions that need actor identity.
- tg-whoami and tg-update-user CLIs.

Spec polish
- iam-contract.md: actor-injection rule documented; whoami /
  bootstrap-status added to operations list; permission-scope
  framing tightened (workspace scope is a property of the grant,
  not the user or role).
- iam.md: self-service section; gateway flow gains the actor-
  injection step; role section reframed so iam-svc constraints
  don't leak into contract-level prose.
- iam-protocol.md: ops table updated for whoami, bootstrap-status,
  optional-workspace pattern; bootstrap_available added to the
  IamResponse listing.

trustgraph-cli/pyproject.toml

@@ -44,6 +44,8 @@ tg-bootstrap-iam = "trustgraph.cli.bootstrap_iam:main"
 tg-login = "trustgraph.cli.login:main"
 tg-create-user = "trustgraph.cli.create_user:main"
 tg-list-users = "trustgraph.cli.list_users:main"
+tg-whoami = "trustgraph.cli.whoami:main"
+tg-update-user = "trustgraph.cli.update_user:main"
 tg-disable-user = "trustgraph.cli.disable_user:main"
 tg-enable-user = "trustgraph.cli.enable_user:main"
 tg-delete-user = "trustgraph.cli.delete_user:main"