feat: resolve agent workspace from session/project/fallback

Heartbeat service resolves cwd from task session, project primary
workspace, or agent home directory (~/.paperclip/instances/.../workspaces/).
Adapters receive workspace context and forward it as env vars and
session params. cwd is now optional in adapter config.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/agent-config-primitives.tsx

@@ -15,7 +15,7 @@ export const help: Record<string, string> = {
   reportsTo: "The agent this one reports to in the org hierarchy.",
   capabilities: "Describes what this agent can do. Shown in the org chart and used for task routing.",
   adapterType: "How this agent runs: local CLI (Claude/Codex), spawned process, or HTTP webhook.",
-  cwd: "The working directory where the agent operates. Use an absolute path on the machine running Paperclip.",
+  cwd: "Default working directory fallback for local adapters. Use an absolute path on the machine running Paperclip.",
   promptTemplate: "The prompt sent to the agent on each heartbeat. Supports {{ agent.id }}, {{ agent.name }}, {{ agent.role }} variables.",
   model: "Override the default model used by the adapter.",
   thinkingEffort: "Control model reasoning depth. Supported values vary by adapter/model.",