Address P2/P3: fix REGISTRY replicate list, update stale error message

- Replace LinearRegression (internal helper) with StaggeredTripleDifference
  (public estimator) in REGISTRY.md replicate-weight support matrix
- Update wild bootstrap + survey error message to remove stale "planned
  Phase 5 support" reference

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: igerber

diff_diff/survey.py

@@ -1087,8 +1087,8 @@ def _resolve_survey_for_fit(survey_design, data, inference_mode="analytical"):
     if inference_mode == "wild_bootstrap":
         raise NotImplementedError(
             "Wild bootstrap with survey weights is not yet supported. "
-            "Use inference='analytical' with survey_design, or see "
-            "docs/survey-roadmap.md for planned Phase 5 support."
+            "Use inference='analytical' with survey_design, or use "
+            "survey-aware multiplier bootstrap (n_bootstrap > 0)."
         )
 
     resolved = survey_design.resolve(data)

docs/methodology/REGISTRY.md

@@ -2307,11 +2307,11 @@ variance from the distribution of replicate estimates.
   design structure is fixed and dropped replicates contribute zero to the
   sum without changing the scale. Survey df uses `n_valid - 1` for
   t-based inference.
-- **Note:** Replicate-weight support matrix (12 of 15 estimators):
+- **Note:** Replicate-weight support matrix (12 of 15 public estimators):
   - **Supported**: CallawaySantAnna (reg/ipw/dr with or without covariates,
     no bootstrap; IF-based replicate variance is covariate-agnostic),
     ContinuousDiD (no bootstrap), EfficientDiD (no bootstrap),
-    TripleDifference (all methods), LinearRegression (OLS path),
+    TripleDifference (all methods), StaggeredTripleDifference (IF-based),
     DifferenceInDifferences (no-absorb via LinearRegression dispatch,
     absorb via estimator-level refit), MultiPeriodDiD (no-absorb via
     `compute_replicate_vcov`, absorb via estimator-level refit),