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/cli/src/__tests__/resolve-head-hash.test.ts

@@ -12,7 +12,7 @@ beforeEach(async () => {
   tmpDir = await mkdtemp(join(tmpdir(), "cli-uwf-resolve-head-"));
   const casDir = join(tmpDir, "cas");
   await mkdir(casDir, { recursive: true });
-  process.env.OCAS_DIR = casDir;
+  process.env.OCAS_HOME = casDir;
 });
 
 afterEach(async () => {