refactor(cli/fix): migrate to CommandOutput with markdown rendering

Convert cli/fix from 20+ imperative log calls to structured FixResult
data returned via CommandOutput.

Changes:
- Define FixIssue and FixResult types for structured diagnostic output
- All handler functions (ownership, permissions, schema) now return
  arrays of FixIssue objects instead of logging directly
- Add formatFixResult() human formatter with per-category sections,
  status markers (✓/✗/•), and instructions blocks
- Use OutputError for failure cases (renders data then exits code 1)
- --json and --fields flags now supported automatically
- Tests updated to assert on rendered stdout instead of consola stderr

Author: BYK