fix: clarify managed oxfmt config generation

[exKAZUu]

Summary

• Replace the ambiguous generic tool config content generator with oxfmt-specific config generation in oxfmtConfig.ts
• Add wbfy managed oxfmt-base and oxfmt-export markers to generated oxfmt configs, matching the oxlint config update pattern
• Extract shared managed-block replacement behavior into ManagedConfigBlocks and reuse it from both oxfmt and oxlint generators
• Keep generated CommonJS oxfmt wording specific to oxfmt .ts auto-discovery

Why

• The old generateToolConfigContent name implied broader tool support than it actually provided
• Oxfmt config should preserve user-owned content around managed sections the same way oxlint config does
• A small class removes repeated marker/tool arguments while keeping tool-specific behavior explicit at each generator

Testing

• yarn verify

Notes

• yarn verify still reports four existing unrelated oxlint warnings in packages/wbfy; no new warnings or errors were introduced

[gemini-code-assist]

Code Review

This pull request refactors the configuration generation logic by replacing the generic toolConfigContent.ts with a specialized oxfmtConfigContent.ts and a shared configContent.ts for content normalization. It updates the oxfmtConfig and oxlintConfig generators to utilize these new modules, improving modularity. I have no feedback to provide.