docs: add FAQ on TiDB X and Dedicated Projects, detailing changes and instance migration requirements

Author: awxxxxxx

tidb-cloud/tidbx-instance-move-faq.md

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+# TiDB X Project and Dedicated Project: What Changed and Why Instances Need to Move
+
+## What Changed
+
+TiDB Cloud now introduces **typed projects** to provide a clearer separation between different product tiers. Projects are classified into two distinct types:
+
+- **TiDB X Project** — designed for TiDB Cloud X instances (Starter, Essential, Premium)
+- **Dedicated Project** — designed for TiDB Cloud Dedicated clusters
+
+Each project type can **only host its own resource type**:
+
+- A TiDB X Project can only contain TiDB X instances.
+- A Dedicated Project can only contain Dedicated clusters.
+
+This typed project model maintains a consistent **Organization → Project → Resource** hierarchy across all tiers, while allowing each product line to evolve with its own project behavior and capabilities.
+
+## Why Two Project Types
+
+TiDB X Projects and Dedicated Projects serve different use cases and have different characteristics:
+
+| Capability | TiDB X Project | Dedicated Project |
+|---|---|---|
+| Project Settings | ❌ | ✅ |
+| Project-level RBAC | ✅ | ✅ |
+| Billing Aggregation | ✅ | ✅ |
+| Move instances between projects | ✅ | ❌ |
+| Project is optional | ✅ (instances can exist at org level) | ❌ (clusters must belong to a project) |
+| Resource type | TiDB X instances only | Dedicated clusters only |
+
+### TiDB X Project
+
+- **Lightweight and optional**. TiDB X users can create instances without assigning them to a project. Projects become useful when users want to organize and group resources, but are not required.
+- **Instance mobility**. TiDB X instances can be moved between TiDB X Projects or back to the organization level, giving users flexibility in how they organize their resources.
+
+### Dedicated Project
+
+- **Mandatory project membership**. Every Dedicated cluster must belong to a Dedicated Project.
+- **No instance mobility across projects**. Dedicated clusters cannot be moved between projects due to their infrastructure bindings.
+
+## Why Instances Need to Move
+
+Before this change, a single project could contain both Dedicated clusters and TiDB X instances (Starter, Essential). With the introduction of typed projects, this mixed state is no longer supported.
+
+**If a Dedicated Project currently contains TiDB X instances (Starter or Essential), those instances need to be moved out.**
+
+This is because:
+
+1. **Each project type now exclusively hosts its own resource type.** A Dedicated Project can only contain Dedicated clusters, and a TiDB X Project can only contain TiDB X instances.
+2. **TiDB X instances and Dedicated clusters have different project behaviors.** TiDB X instances benefit from lightweight, optional project membership and instance mobility — capabilities that do not apply within a Dedicated Project.
+3. **Keeping them separated ensures a consistent experience.** Users interacting with a Dedicated Project expect Dedicated-specific settings and behaviors. Mixing resource types would create confusion around which capabilities apply.
+
+## What Happens When Instances Are Moved
+
+When TiDB X instances are moved out of a Dedicated Project:
+
+- The instances are moved to a **TiDB X Project**.
+- **No data or service disruption** is expected. This is a resource re-organization action, not an infrastructure change.
+- After the move, users manage their TiDB X instances through TiDB X Projects (or at the org level), and their Dedicated clusters continue to be managed through Dedicated Projects.
+
+## Summary
+
+| Before | After |
+|---|---|
+| A single project could contain both Dedicated clusters and TiDB X instances | Each project type exclusively hosts its own resource type |
+| TiDB X instances in Dedicated Projects inherited Dedicated project behaviors | TiDB X instances are managed in TiDB X Projects with their own lightweight model |
+| No distinction between project types | Clear separation: TiDB X Project vs Dedicated Project |
+
+This change gives each product tier a project model that fits its own needs, while keeping the overall organization structure consistent and predictable.