ci: discover OpenVSCode web assets for GHCR image

[tariqsaidofficial]

Fixes the WPCodeSpace OpenVSCode GHCR image assembly by building/discovering the actual OpenVSCode browser web assets required by the running web server.

Problem:

• The first published image responded over HTTP but rendered a blank page.
• Container logs showed missing /opt/openvscode-server/out/vs/code/browser/workbench/workbench.css and /opt/openvscode-server/out/nls.messages.js.
• Copying repository out/. was insufficient because that output had server-main.js but not packaged web client assets.

Changes:

• Add the official vscode-web-min-ci build step.
• Locate runtime and web asset candidates during CI.
• Select a web asset source that actually contains workbench.css and nls.messages.js.
• Copy the selected web assets into the Docker context.
• Validate required assets in Docker context.
• Validate required assets inside the built image.
• Curl required browser assets during smoke test.
• Fail on missing asset logs.

Preserved:

• No pull_request trigger.
• No latest tag.
• Immutable tags only.
• YAML-safe Dockerfile generation.
• Generated bundle guard.

Local validation:

• YAML parsed successfully.
• No pull_request or latest match.
• Workflow-only diff.
• git diff --check passed.