feat(client-portal) : phase 1 foundations — ROLE_CLIENT hardening + ClientTicket (back)

LST-69 (3.2) phase 1. New ClientPortal module + security foundations for the
client portal (spec docs/superpowers/specs/2026-03-15-client-portal-design.md).

- Security: User::getRoles() no longer adds ROLE_USER to ROLE_CLIENT users;
  role_hierarchy ROLE_ADMIN: [ROLE_USER, ROLE_CLIENT]. Existing Task/Project/
  Client/TimeEntry/metadata endpoints already required ROLE_USER -> a pure
  ROLE_CLIENT is walled off (verified: 403).
- User (Core): client (ManyToOne ClientInterface, SET NULL) + allowedProjects
  (ManyToMany ProjectInterface). UserInterface extended (getClient/
  getAllowedProjects).
- New ClientTicket entity (module ClientPortal) + enums + repository + API with
  per-client isolation (ClientTicketProvider: own tickets ∩ allowedProjects),
  per-project numbering under advisory lock (rejects if user.client null),
  status transition rules. ClientTicketInterface contract for Task/TaskDocument.
- TaskDocument generalized: task nullable + clientTicket (CASCADE) + CHECK;
  per-role access. Task.clientTicket exposed in task:read.
- Additive migration; demo client fixtures.
- Tenancy tests assert the isolation invariant (a client never sees another
  client's tickets) rather than brittle absolute counts (shared test DB).

178 tests green, mapping valid, cs-fixer clean.

config/packages/security.yaml

@@ -1,6 +1,6 @@
 security:
     role_hierarchy:
-        ROLE_ADMIN: [ROLE_USER]
+        ROLE_ADMIN: [ROLE_USER, ROLE_CLIENT]
 
     # https://symfony.com/doc/current/security.html#registering-the-user-hashing-passwords
     password_hashers: