Add Skills Library source filters

[brsbl]

Summary

• add independent Included and BB official source toggles to the Skills Library
• default BB official on and Included off
• combine enabled attributed sources while leaving user and project skills unaffected
• preserve existing provider filtering, search, sorting, pagination, and rows

Verification

• 26 focused Skills tests passed
• Turbo typecheck passed for @bb/app
• branch dev app verified default BB-official, both-enabled, and Included-only states

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