CDK LSP Server and Web Explorer

## Description

A language server (`cdk lsp`) and browser-based explorer (`cdk explore`) that surface construct-to-resource mappings, validation diagnostics, and three-way linked navigation between CDK source code, construct trees, and CloudFormation templates.

## Roles

| Role | User
|---------------------|------------------------------
| Proposed by | @megha-narayanan
| Author(s) | @megha-narayanan
| API Bar Raiser | @ShadowCat567
| Stakeholders |

## Workflow

- [x] Tracking issue created (label: `status/proposed`)
- [x] API bar raiser assigned (ping us at [#aws-cdk-rfcs](https://cdk-dev.slack.com/archives/C025ZFGMUCD) if needed)
- [x] Kick off meeting
- [x] RFC pull request submitted (label: `status/review`)
- [x] Community reach out (via Slack and/or Twitter)
- [x] API signed-off (label `status/api-approved` applied to pull request)
- [x] Final comments period (label: `status/final-comments-period`)
- [x] Approved and merged (label: `status/approved`)
- [x] Execution plan submitted (label: `status/planning`)
- [x] Plan approved and merged (label: `status/implementing`)
- [ ] Implementation complete (label: `status/done`)

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Start by reading the approved RFC and merged execution plan for the proposed `cdk lsp` and `cdk explore` commands. The work is done when implementation is complete, including construct-to-resource mappings, validation diagnostics, and linked navigation between CDK source, construct trees, and CloudFormation templates.

Written by the indexing model from the issue text.