pstA curation notes

• Q88JJ1 is the PP_2658 membrane subunit of the PP_2656-PP_2659 Pst-like
  operon. Its phosphate-permease role is homology-derived, and the collective
  transporter activity is modeled with contributes_to rather than enables.
  [file:PSEPK/pstA/pstA-uniprot.txt, "RecName: Full=Phosphate transport system permease protein PstA"]
• The completed pathway/taxon report treats PP_2656-PP_2659 as a second
  complete Pst-like operon lacking the Pho-linked context of PP_5326-PP_5329;
  its physiological trigger remains unresolved. [file:projects/P_PUTIDA/deep-research/PSEPK__bacterial_pst_phosphate_uptake__ppu02010-deep-research-openscientist.md,
  "NO phoU/phoBR neighbours"]
• The PRS2000 Pst study is same-species pathway evidence, not direct evidence
  for Q88JJ1 or KT2440. PMID:16232467