docs(showcase): add public qlockify showcase + screenshots

docs/demo-guide.md

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+# Demo Guide
+
+Qlockify includes a public demo flow for exploring the product without accessing real customer data.
+
+## How to Try It
+
+1. Open [https://qlockify.ir](https://qlockify.ir).
+2. Use the demo call-to-action on the landing page.
+3. The app creates a temporary isolated workspace and logs you in as the demo owner.
+4. Explore timesheets, clients, projects, tags, access management, and reports.
+
+## Demo Data
+
+The demo workspace includes realistic sample data such as:
+
+- workspace members
+- clients and projects
+- tags
+- time entries
+- billable work
+- hourly rates
+- project access rules
+- reportable activity
+
+## Isolation
+
+Each demo visitor gets a separate demo environment. Actions in one demo do not affect other demo users or production users.
+
+## Expiration
+
+Demo environments are temporary and are cleaned automatically. Do not enter sensitive or real customer data in the demo.
+