fix(fp): resolve dormant code and adopt lifecycle markers

[netravnen]

Applies what remains of the ratified fp triage now that the write-guard
work has landed on dev-next. An earlier draft of this change staged
FP's exclusion cluster as planned safety code with @staged wip
markers; that cluster is now live upstream -- wired into the IX-F
netixlan write paths and shared via lib/admincom-entity-exclusions.js
-- and under the ratified @StaGeD grammar (markers only on
unreferenced symbols) staging no longer applies, so those markers are
dropped here rather than carried. What remains are the orphan
deletions and the tree's first @deprecated adopters under the frozen
grammar.

Changes:

• Delete groupCustomItemsByVisualRow (orphaned by the 7169919 toolbar
  refactor).
• Delete the dead members array population in copy-user-roles; the
  admins-only clipboard output is byte-identical.
• Delete FP's unused buildTampermonkeyRequestHeaders copy -- the
  identical body survives in CP and DP, and a hoped-for lib extraction
  is not a planned FP feature.
• Convert LEGACY_API_PAYLOAD_CACHE_STORAGE_PREFIX and
  LEGACY_API_PAYLOAD_TAB_CACHE_STORAGE_PREFIX to the frozen
  @deprecated — <reason; removal condition> line-comment form,
  preserving the migrateLegacyApiPayloadCacheKeys() sweep prose.
• Bump FP @Version to 1.1.42 (src + meta); regenerate .user.js.

Testing:

• Full suite green: 585 pass, 0 fail (1 pre-existing skip).
• build --check and node --check on the regenerated .user.js: clean.
• Verified by grep across all five source files + tests/ that zero
  references remain to groupCustomItemsByVisualRow,
  buildTampermonkeyRequestHeaders (FP copy) and the members array.

Backwards Compatibility:

• copy-user-roles output unchanged (admins joined by newline).
• No live user-facing behavior changes; deleted code had no caller.