Copy-edit paper: fix figure name, citation, abbreviations, prose

[neuromechanist]

Comprehensive copy-edit pass on paper.md after several defects were spotted post-merge (the earlier review was scoped to word-count cuts, not proofreading). Driven by an exhaustive manuscript:paper-review copy-edit plus a verification of the two competitor packages against their actual repos.

Substantive fixes

• Figure carried the old pyAMICA/NG name. Regenerated multimodel-ensemble.png from the cached ensemble (no re-fitting); verified visually it now reads pamica in the title, both legends, and stats boxes.
• Citation error I introduced during the trim: the foundational AMICA reference @palmer2012amica had lost its only citation (orphaned in the bib), and the Acknowledgements' "Palmer et al., cited above" pointed at the Newton-method paper instead. Now cited at AMICA's first mention and in the Acknowledgements; orphan-check confirms every bib entry is cited.
• Competitor-claim accuracy: verified amica (Esmaeili, JAX) and pyamica (Herforth, PyTorch) are both multi-model and MNE-compatible (paper's claims hold), but softened "validation beyond what either alternative publishes" to a factual statement of pamica's specific validation, since Esmaeili's package does publish MATLAB-AMICA parity and I can't verify relative depth.
• Table 1 header claimed "correlation / Amari distance" but 2 of 5 rows are neither; changed to "Result (mean)".

Grammar / abbreviations / prose

• Fixed "sources, which isolates" (agreement), the "its" MNE-Python antecedent slip, a dangling "once well-determined", and an unanchored "faster ICA".
• Defined CPU, GPU, EM, MKL, LL (spelled out), and sd (glossed); disambiguated "permutation" (Amari invariance vs the permutation test).
• Removed repeated-conjunction runs (three "and"s in the EEGLAB sentence and the Acknowledgements; three "which"es already fixed), the redundant library list, and softened "catch"->"match", "leads with"->"offers".
• Statement of need no longer opens with "also"; consecutive "AMICA's" openers smoothed.

Body 1512 words, no em-dashes; Draft PDF CI validates the build.