Move direct deployment engine to public preview (#4888)

## Changes
- Move the direct deployment engine status from "experimental" to
"public preview".
- Remove the experimental warning from `databricks bundle deployment
migrate` command.
- Update `docs/direct.md` status line.

## Why
The direct deployment engine has matured enough for public preview.
Removing the experimental warnings reflects this and encourages broader
adoption beyond development-only targets.

Author: denik

NEXT_CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Release v0.296.0
 
 ### Notable Changes
+* Direct deployment engine for DABs is now in Public Preview. Documentation at [docs/direct.md](docs/direct.md).
 
 ### CLI
 * Auth commands now error when --profile and --host conflict ([#4841](https://github.com/databricks/cli/pull/4841))

acceptance/bundle/help/bundle-deployment-migrate/output.txt

@@ -8,8 +8,6 @@ lineage and incremented serial number.
 Note, the migration is performed locally only. To finalize it, run 'bundle deploy'. This will synchronize the state file
 to the workspace so that subsequent deploys of this bundle use direct deployment engine as well.
 
-WARNING: Both direct deployment engine and this command are experimental and not recommended for production targets yet.
-
 Usage:
   databricks bundle deployment migrate [flags]
 

cmd/bundle/deployment/migrate.go

@@ -133,8 +133,6 @@ lineage and incremented serial number.
 
 Note, the migration is performed locally only. To finalize it, run 'bundle deploy'. This will synchronize the state file
 to the workspace so that subsequent deploys of this bundle use direct deployment engine as well.
-
-WARNING: Both direct deployment engine and this command are experimental and not recommended for production targets yet.
 `,
 		Args: root.NoArgs,
 	}

docs/direct.md

@@ -1,6 +1,6 @@
 ## Status
 
-Status: experimental, only recommended for development targets or evaluation, not for production use.
+Status: Public Preview.
 Known issues: https://github.com/databricks/cli/issues?q=state%3Aopen%20label%3Aengine%2Fdirect
 
 ## Reporting bugs