Move polyglot SDK validation tests to CLI E2E test infrastructure

## Problem

The polyglot SDK validation tests (`.github/workflows/polyglot-validation.yml`) run as standalone Docker builds in CI. These tests are fragile because they build Docker images that run `apt-get` and `curl` against external package mirrors, which frequently fail with transient errors (504s, digest mismatches, timeouts).

Example failure from https://github.com/microsoft/aspire/actions/runs/24609589983/job/71961739197:
```
#8 0.165 curl: (22) The requested URL returned error: 504
Process completed with exit code 4.
```

These tests consistently fail across unrelated PRs due to infrastructure issues, blocking merges.

## Proposal

Move the polyglot SDK validation tests (Python, Java, Go, Rust, TypeScript) to the CLI E2E test infrastructure (`Aspire.Cli.EndToEnd.Tests`). This would:

- Use the existing Hex1b terminal automation for consistent test execution
- Share the CLI E2E Docker base image instead of building separate images per language
- Benefit from retry logic and better error reporting in the E2E framework
- Reduce CI flakiness from transient network failures during Docker builds
- Align with how other CLI-driven tests are structured