fix(cli): add agents project switch command to project CLI

Implements the agents project switch <name> command to switch the active
project context, bringing the CLI into compliance with the CleverAgents CLI
spec (v3.2.0+).

Changes:
- Added switch subcommand extracted to src/cleveragents/cli/commands/project_switch.py
  to keep project.py below the 500-line guideline
- Implemented project context switching via ProjectService.set_current_project()
  maintaining the CLI -> Service -> Repository 4-layer architecture boundary
- Added --format flag support (rich, json, yaml, plain) for output formatting
- Implemented appropriate error handling when the project does not exist
- Added BDD feature scenarios and step definitions for the new command
- Updated BDD scenarios to assert context change was persisted via service layer
- Updated CONTRIBUTORS.md with contribution details

Closes #8623

ISSUES CLOSED: #8623

features/steps/plan_phase_migration_steps.py

@@ -113,7 +113,11 @@ def step_insert_plan_with_phase_and_state(context: Any, phase: str, state: str)
 def step_try_insert_plan_with_phase_and_state(
     context: Any, phase: str, state: str
 ) -> None:
-    """Try to insert a plan with the specified phase and state, expecting failure."""
+    """Try inserting a plan without ORM defaults to exercise the phase constraint.
+
+    The direct SQL insert must provide both plan_id and root_plan_id so the
+    phase constraint is validated instead of failing on missing root_plan_id.
+    """
     session: Session = context.phase_rebaseline_session
     ulid = _next_ulid()
     now = _now_iso()
@@ -121,14 +125,15 @@ def step_try_insert_plan_with_phase_and_state(
         session.execute(
             text(
                 "INSERT INTO v3_plans "
-                "(plan_id, action_name, namespaced_name, namespace, "
+                "(plan_id, root_plan_id, action_name, namespaced_name, namespace, "
                 "phase, processing_state, description, tags_json, "
                 "created_at, updated_at) "
-                "VALUES (:pid, :aname, :nname, :ns, :phase, :state, "
+                "VALUES (:pid, :rpid, :aname, :nname, :ns, :phase, :state, "
                 ":desc, :tags, :cat, :uat)"
             ),
             {
                 "pid": ulid,
+                "rpid": ulid,
                 "aname": "local/phase-test-action",
                 "nname": "local/try-plan",
                 "ns": "local",