README commands and official links point to moved paths

### Description

Several localized README surfaces contain copy-paste paths or official-documentation links that now resolve to nonexistent targets. These are confirmed path mismatches rather than authentication-only or transient link-check failures.

Affected groups at commit `0890278a6571e4190c1ab8cacd9becc147f74d9c`:

1. Four Skills Sandbox READMEs under `veadk_0_x_x` and `veadk_1_x_x` use hyphenated directory names (`veadk-0.x.x` / `veadk-1.x.x`) in their trees, `cd` commands, and six GitHub file links. The tracked directories use underscores, so the commands enter nonexistent paths and the GitHub links return 404.
2. `python/01-tutorials/01-agentkit-runtime/a2a_simple/README.md` and `README_en.md` link to `https://github.com/google/adk`, which returns 404. The official Python ADK repository is `https://github.com/google/adk-python`.
3. `image_video_tools/README.md` and `README_en.md` link to the removed VeADK `/tools/builtin/` route.
4. `video_breakdown_agent/docs/README_CONFIG.md` links to removed VeADK `/configuration/` and `/observability/` routes. The current VeADK documentation publishes these under `/cn/docs/references/configuration/` and `/cn/docs/framework/observability/`.

### Reproduction

- Resolve the Skills Sandbox `cd` and GitHub paths against the tracked tree: only the underscore directories exist.
- Open the Google ADK URL: the old repository is 404 while `google/adk-python` is the current official project.
- Open the three old VeADK route families: they return the site's 404 page; the current `/cn/docs/...` routes return documentation pages.

### Expected behavior

Copy-paste commands should reference tracked directories, localized copies should remain consistent, and official links should target the current canonical documentation/project pages.

### Impact

Users cannot follow the documented Skills Sandbox commands and are sent to 404 pages for referenced source files, the ADK project, and VeADK configuration/tool/observability documentation.

### Duplicate check

Open/closed issues, all PR states, commit history, and exact old paths were searched. PRs #237 and #239 repaired other documentation paths but not these targets. No active equivalent issue or PR was found.

Check the four Skills Sandbox READMEs under veadk_0_x_x and veadk_1_x_x, plus python/01-tutorials/01-agentkit-runtime/a2a_simple/README.md, README_en.md, image_video_tools/README.md, README_en.md, and video_breakdown_agent/docs/README_CONFIG.md. Compare every affected path with the tracked tree and current URLs. Done means commands use underscore directories, localized files stay consistent, and all listed links resolve to the canonical project or documentation pages.

Written by the indexing model from the issue text.