docs: link to the code in the example repository and the modules

[dsalaj]

Adds links from the docs to the exact lines they describe, like CONSUMER_ROLE in the example's functional_roles.tf, the access role privilege maps, the MCP server snowflake_execute, the procedure's error handling, etc.

The file tree on the landing page is now a table, so each file can link to the example repo.

Module links point at the tags the docs pin (access_roles 0.0.2, logical_import_layer 0.0.5) and example links point at the current main commit, so line numbers won't drift when the code changes. All links return 200.

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