feat: add config init scaffolding and shared config file writer

[jy-tan]

Summary

Add a first-class fence config init flow to bootstrap usable config files and refactor config JSON/file rendering into internal/config so both init and import share the same writer primitives while preserving import-specific output behavior.

Resolves #34.

Changes

• Add fence config init with support for --template, --minimal, --output, --force, and --print.
• Add --scaffold mode to generate properly indented JSON with empty hint arrays for editable sections.
• Add init-specific top-of-file guidance comments (distinct wording from import comments) for files written by config init.
• Refactor config file rendering/writing into internal/config/config_file.go via shared APIs (MarshalConfigJSON, FormatConfigForFile, WriteConfigFile).
• Keep fence import behavior stable by retaining importer wrappers and import-specific header comments while delegating rendering/writing to internal/config.
• Add/expand tests in cmd/fence/main_test.go and new internal/config/config_file_test.go; update docs in README.md and docs/quickstart.md.

[cubic-dev-ai]

2 issues found across 7 files

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="internal/config/config_file.go">

<violation number="1" location="internal/config/config_file.go:30">
P2: Filesystem config serialization drops AllowRead/AllowExecute/DefaultDenyRead/WSLInterop, so writing a config will silently lose these settings. Include these fields in the clean filesystem struct and update the empty-check logic to preserve them.</violation>

<violation number="2" location="internal/config/config_file.go:45">
P2: SSH configuration is never serialized, so any SSH rules in a config are silently lost when writing the file. Add a clean SSH struct and include cfg.SSH in MarshalConfigJSON/empty checks.</violation>
</file>

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