[Docs]: Add privacy policy and terms of service for marketplace - #64

Add Privacy Policy and Terms of Service

Adds PRIVACY.md and TERMS.md at the repo root, required for Marketplace submission (the review team needs valid links for both before an app can be approved).

What's covered

• PRIVACY.md: explains that Apps.SpamMonitor runs entirely inside the customer's own Rocket.Chat instance, what data it reads/stores (message metadata, spam-status data, admin config), that everything stays in the instance's own persistence layer, and that no data is sent to any third party.
• TERMS.md: acceptance, what the app does, support model (best-effort via GitHub Issues, no SLA), no-warranty / limitation-of-liability, and termination terms.

Open item — needs a decision before merging to a release used for submission

TERMS.md §3 (License) is currently a TODO — this repo doesn't have a chosen license yet. @alfredo, can we confirm which license we're using (MIT?) so we can add a LICENSE file and fill in that section? Don't want this going out to Marketplace review with it still open.

Notes

• Both files are plain markdown so GitHub renders them directly — that satisfies the Marketplace review requirement of a working link, no external hosting needed.
• Once merged, the Marketplace submission form's "Privacy policy" and "Terms of Service" URL fields can point to:
  • https://github.com/RocketChat/Apps.SpamMonitor/blob/main/PRIVACY.md
  • https://github.com/RocketChat/Apps.SpamMonitor/blob/main/TERMS.md