docs(guides): add two testcontainers intro guides (go and python) (#24450)

## Description

Migrate the first two Testcontainers getting-started guides from
[testcontainers.com/guides](https://testcontainers.com/guides/) into the
Docker docs site:

- **Getting started with Testcontainers for Go** — multi-page guide with
4 chapters (create project, write tests, test suites, run tests). Code
updated to testcontainers-go v0.41.0 API (`postgres.Run()`,
`CleanupContainer`, `BasicWaitStrategies()`).
- **Getting started with Testcontainers for Python** — multi-page guide
with 3 chapters (create project, write tests, run tests). Code updated
to testcontainers-python 4.14.2 (fixed `get_exposed_port()` returning
`int`).

Each guide appears as its own entry in the `/guides/` listing with
proper language and tag filters (`testing-with-docker`). Chapters render
with stepper navigation in the sidebar.

Also adds:
- A `testing-with-docker` tag to `data/tags.yaml`
- A Claude skill
(`.claude/skills/testcontainers-guides-migrator/SKILL.md`) that
documents the repeatable migration process for the remaining 19 guides
- Links from `content/manuals/testcontainers.md` to the new guides
- Vale vocabulary entries for `pgx`, `Micronaut`, `psycopg`, `pytest`

All guide code was compiled and tests verified passing in containers
with Docker socket mounted.

## Related issues or tickets

No related issues found.

## Reviews

- [ ] Technical review
- [ ] Editorial review
- [ ] Product review

_vale/config/vocabularies/Docker/accept.txt

@@ -167,11 +167,14 @@ Paketo
 PAT
 perl
 pgAdmin
+pgx
 PKG
 plaintext
 plist
 pluggable
 Postgres
+psycopg
+pytest
 PowerShell
 Python
 Qualcomm