Prepare for 0.14.0 release

[tsalo]

Note

Prepares the 0.14.0 release with updated metadata and changelog.

• Update CITATION.cff to version: 0.14.0 with date-released: '2026-01-06'
• Add 0.14.0 section to docs/changes.md highlighting:
  • pconn.nii generation from concatenated CIFTI time series
  • parameter to control run-wise correlations
  • --skip flag to omit selected postprocessing outputs
  • support for BIDS proc-<label> entity and cleanup of mode differences docs
  • acknowledgment of a new contributor and full changelog link
• Normalize prior release entries by adding dates/headings for historical versions

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