chore(todo): prune completed-vcov-initiative leftovers + audit-verified stale rows

Cleanup of TODO.md now that the vcov_type threading initiative is complete (all 8
standalone estimators merged, TwoStageDiD #498 last). TODO.md only — no methodology
or source changes.

Compact prune of the completed initiative's leftovers:
- the `| Done |` umbrella row + its orphan blank lines (rejoins the methodology
  table to its header), the Tier B threading bullet, and the stale duplicate
  TwoStageDiD-Conley row whose "`__init__` lacks `vcov_type`" premise is false post-#498
- the "Rows 104-105 LIFTED" comment block, the two ~~LIFTED~~ weighted-BM rows, and
  the Tier C LIFTED bullet (clubSandwich WLS-CR2 port, #475)
- two resolved-marker HTML comments (WooldridgeDiD cohort_share; PreTrendsPower)
- rewrote the Standard Error Consistency prose to "complete" and repointed its
  weighted-CR2 gate at the open multi-absorb row

Staleness audit of the ~50 remaining follow-up rows (5 subagents; every finding
re-verified against current source before acting -- the vast majority are genuine
open deferrals):
- removed the `bias_corrected_local_linear: weights=` row (shipped; residual
  unweighted-DPI gap already tracked by the sibling row) and narrowed the Tier D
  lprobust bullet's stale `weights` -> `weight-aware auto-bandwidth DPI`
- removed the `compute_survey_metadata`/`raw_w_for_meta` dedup row (done via the
  shared `survey._resolve_survey_for_fit` helper)
- tightened the HAD Phase-4.5-C survey-aware-pretests row: dropped the shipped
  pweight+PSU+FPC+strata narration, kept the two open items (replicate-weight
  designs; lonely_psu='adjust'+singleton on the Stute family)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: igerber