refactor: unify env vars (UWF_HOME, OCAS_HOME) + env only in CLI (#37)

Breaking changes:
- UWF_STORAGE_ROOT → UWF_HOME
- WORKFLOW_STORAGE_ROOT removed (no fallback)
- OCAS_DIR → OCAS_HOME (aligned with ocas CLI)

Library functions no longer read process.env:
- util-agent/storage.ts: resolveStorageRoot(override), getGlobalCasDir(override)
- agent-hermes: isResumeDisabled(flag) pure function, CLI reads env
- agent-claude-code: CLI reads CLAUDE_MODEL and passes to agent

Fixes #37

packages/agent-builtin/__tests__/prompt.test.ts

@@ -29,6 +29,8 @@ function minimalContext(overrides: Partial<AgentContext> = {}): AgentContext {
     outputFormatInstruction: "---\nstatus: done\n---",
     edgePrompt: "Implement the fix described in the plan.",
     isFirstVisit: true,
+    storageRoot: "/tmp/uwf-test",
+    casDir: "/tmp/ocas-test",
     ...overrides,
   };
 }