More consistent document crate names

[timon-schelling]

[workspace.dependencies]
...
document-graph-storage = { path = "document/graph-storage", default-features = false }
document-format = { path = "document/format" }
document-container = { path = "document/container" }
...

[gemini-code-assist]

Code Review

This pull request renames the graph-storage crate to document-graph and updates all references, imports, and documentation across the codebase to reflect this change. The review feedback identifies minor layout alignment issues in the ASCII art diagrams within the document-format.md RFC document caused by the difference in name lengths, and provides suggestions to correct the formatting.

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[cubic-dev-ai]

Review completed against the latest diff

Confidence score: 5/5

• Safe to merge after the addressed issues were fixed.

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>