docs: mention 24h as a valid --window alias in now/tui help

[chayu163]

Summary

• Mentions 24h as a valid --window alias in the now and tui help text (src/agentacct/cli.py:9184,9429), matching the NOW_WINDOW_ALIASES entry that already accepts it.

Fixes #206

Test plan

• pytest -q
• Secret scan
• No paid provider calls

Safety checklist

• Preserves local-first behavior
• Does not store API keys or secrets
• Does not expose localhost services publicly by default
• Does not control processes agentacct did not start
• Provider/API forwarding remains opt-in and budget-gated
• JSON output paths remain machine-readable when --json is used

Docs

• Help text only — no README change
• Public docs avoid private strategy/roadmap claims