Clarify destination secrets docs

[cookesan]

Summary

• Document the exact secrets file lookup order with and without destinations.
• Clarify that .kamal/secrets is not read when a destination is selected.
• Add the destination note to the generated docs source and the init secrets template.
• Include the existing output docs page in the docs generator map so all configuration docs sources can be generated.

Testing

• tmpdir=$(mktemp -d); mkdir -p "$tmpdir/docs/configuration"; ruby bin/docs "$tmpdir"
• ruby -c bin/docs
• git diff --check
• Not run: Ruby unit tests; the local Ruby toolchain does not match the lockfile.

[Copilot]

Pull request overview

This PR updates Kamal’s configuration documentation and templates to accurately describe secrets file lookup order, especially when using destinations, and ensures the docs generator includes all configuration doc sources.

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Changes:

• Clarify secrets lookup/override order for both destination and non-destination deploys.
• Add destination-specific note to the init secrets template.
• Include the existing output docs source in bin/docs generation map.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
lib/kamal/configuration/docs/env.yml	Updates env/secrets documentation to spell out secrets file precedence and destination behavior.
lib/kamal/configuration/docs/configuration.yml	Clarifies how secrets_path maps to -common and destination-specific secrets files.
lib/kamal/cli/templates/secrets	Updates the generated secrets template with guidance for destinations and shared secrets.
bin/docs	Adds output to the docs generator map so output docs are generated.

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[cookesan]

Following up here. The current diff already incorporates the two review notes on env.yml: it now refers to the configured secrets files instead of a single .kamal/secrets file, and it uses <destination> consistently in the destination-specific path examples. If there's anything else you'd like tightened before review, I'm happy to update it.