feat: add two-level work mode (projectExecution + roleExecution) (#15) (#18)

Replaces single 'workMode' with two distinct settings:

1. Plugin-level 'projectExecution' (parallel | sequential)
   - parallel: each project can have active workers independently
   - sequential: only one project can have active workers at a time

2. Project-level 'roleExecution' (parallel | sequential)
   - parallel: DEV and QA can run simultaneously on same project
   - sequential: only one role (DEV or QA) active at a time per project

Changes:
- index.ts: rename workMode → projectExecution in config schema
- projects.ts: add roleExecution field to Project type
- heartbeat_tick: check both levels before picking up tasks
- task_pickup: enforce roleExecution when picking up manually
- project_register: accept roleExecution param (default: parallel)
- devclaw_setup: accept projectExecution param

All defaults remain 'parallel' for backward compatibility.

lib/tools/devclaw-setup.ts

@@ -41,6 +41,11 @@ export function createSetupTool(api: OpenClawPluginApi) {
             qa: { type: "string", description: `QA engineer model (default: ${DEFAULT_MODELS.qa})` },
           },
         },
+        projectExecution: {
+          type: "string",
+          enum: ["parallel", "sequential"],
+          description: "Plugin-level project execution mode: parallel (each project independent) or sequential (work on one project at a time). Default: parallel.",
+        },
       },
     },
 
@@ -49,6 +54,7 @@ export function createSetupTool(api: OpenClawPluginApi) {
       const channelBinding = params.channelBinding as "telegram" | "whatsapp" | undefined;
       const migrateFrom = params.migrateFrom as string | undefined;
       const modelsParam = params.models as Partial<Record<Tier, string>> | undefined;
+      const projectExecution = params.projectExecution as "parallel" | "sequential" | undefined;
       const workspaceDir = ctx.workspaceDir;
 
       const result = await runSetup({
@@ -59,6 +65,7 @@ export function createSetupTool(api: OpenClawPluginApi) {
         agentId: newAgentName ? undefined : ctx.agentId,
         workspacePath: newAgentName ? undefined : workspaceDir,
         models: modelsParam,
+        projectExecution,
       });
 
       const lines = [