refactor(pd): merge cse-pd into pd repository

## Summary

Track the `release-8.5-keyspace` commit batch that has been split into 41 subtasks by functional area.

## Branch

- target branch: `release-8.5-keyspace`
- origin repo: `bufferflies/pd`

## Scope

### mTLS / pd-ctl
- [x] #10531
- [x] #10561
- [x] #10532

### Keyspace / GC
- [x] #10534
- [x] #10566
- [x] #10886
- [x] #10887
- [x] [`f88a4fd9`](https://github.com/bufferflies/pd/commit/f88a4fd923fe5e3724e0d1bea9f03ab4a0b250b8) fix `enable-global-safe-point-v2` init
- [x] [`76277a6b`](https://github.com/bufferflies/pd/commit/76277a6b45d404313da08a71a9d131f341e287e2) create keyspace metrics and logs

### Meta Service Group
- [x] #10596
- [x] #10880
- [x] #10888
- [x] #10889
- [x] #10890
- [x] #10891
- [ ] #10892

### API / Observability
- [x] #10660
- [x] [`a7c733be`](https://github.com/bufferflies/pd/commit/a7c733be11b153b79ea6b1e2a5f848c396f6af5b) add PD API metrics and logs - PR: [#10523](https://github.com/tikv/pd/pull/10523)

### Resource Manager / RU
- [x] #10833
- [x] #10834
- [x] #10838
- [x] #10839
- [x] #10840
- [x] [`71e81850`](https://github.com/bufferflies/pd/commit/71e8185036edbf65d8fd4818ce49594d4df57535) only record active resource group metrics
- [x] [`467deb4f`](https://github.com/bufferflies/pd/commit/467deb4fb47fd152d083e0afa5471a9acec71a1d) only persist states of active resource groups
- [ ] #10872
- [x] [`767c4d30`](https://github.com/bufferflies/pd/commit/767c4d30aae175eb36e7352da9acab852da968f6) modify `resource_manager_resource_unit_service_limit` metric
- [x] [`627dc6ed`](https://github.com/bufferflies/pd/commit/627dc6edaa88482914484f1363e1f4e20f269749) check and add log

### Client / Service Discovery
- [x] #10537
- [x] #10538
- [x] #10539

### Client / Resource Group
- [x] #10557
- [x] #10542

### TSO / Keyspace Group
- [x] #10832
- [x] #10555
- [x] #10554
- [x] #10601
- [x] #10533

### TSO / Client
- [x] #10553
- [x] #10552

## Notes

- Internal execution was split into one parent task plus 41 per-commit subtasks.
- This issue is the umbrella tracker for the full `release-8.5-keyspace` batch.
- Initial audit against `origin/master` on 2026-03-31 found no patch-equivalent fixes for these 41 commits, so all tasks remain open.

This is an umbrella tracker for the release-8.5-keyspace batch rather than a standalone change. Start by reviewing the linked subtasks under their functional areas and the target branch release-8.5-keyspace. It is done when the remaining unchecked subtasks, including #10892 and #10872, are completed and the full batch is merged into the pd repository.

Written by the indexing model from the issue text.