Fix overlapping labels

[EmnaBarbouch]

📑 Summary

Shorten node and relationship labels in the C4 Container demo (demos/c4context.html) to fix overlapping text in rendered diagrams.

Resolves #7492

📏 Design Decisions

Excessively long description strings in Person, System_Ext, Container, ContainerDb, and Rel nodes were causing label overflow and visual overlap in the C4 context and container diagrams. Labels were trimmed to their essential meaning without losing semantic clarity. UpdateRelStyle offset overrides were also removed since they are no longer needed with the shorter labels. One line was added to .gitignore to exclude auto-generated Langium CLI output.

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