chore (region-info): Add AppConfig, Lambda Layers, s3 websites, firehose for `ap-southeast-6` region to `fact-tables.ts`

### Describe the feature

`ap-southeast-6` went live in September of 2025. Since then, several new services have been added. Those services are not present in `fact-tables.ts`.

### Use Case

Our customer was seeing issues deploying firehose delivery streams with error:

````ValidationError: Mapping doesn't contain top-level key 'ap-southeast-6'
at path [EventWebhook/@aws-cdk--aws-kinesisfirehose.CidrBlocks] in aws-cdk-lib.CfnMapping```

### Proposed Solution

Add new services; we are confirming values with service teams. PR incoming.

### Other Information

_No response_

### Acknowledgements

- [x] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS CDK Library version (aws-cdk-lib)

cbf0b03

### AWS CDK CLI version

2.1033.0 (build 1ec3310)

### Environment details (OS name and version, etc.)

Darwin 603e5f78dbc8 24.6.0 Darwin Kernel Version 24.6.0: Wed Nov 5 21:33:32 PST 2025; root:xnu-11417.140.69.705.2~1/RELEASE_ARM64_T6030 arm64

Start by inspecting fact-tables.ts and the existing ap-southeast-6 region entries. Verify the AppConfig, Lambda Layers, S3 website, and Firehose values with the relevant AWS service availability information before adding them. Done means the region has entries for these services and the reported top-level mapping error no longer occurs.

Written by the indexing model from the issue text.