Fix Sphinx -W docstring failure on SyntheticDiD

CI's Sphinx HTML build (-W warnings as errors) failed on f3d5d92 with:

    diff_diff/synthetic_did.py:docstring of diff_diff.synthetic_did.SyntheticDiD:63:
    WARNING: Field list ends without a blank line; unexpected unindent. [docutils]

The Conley-rejection block I added in 8ab51c4 used a custom section header
"Notes (Conley spatial-HAC rejection)" with a parenthetical suffix. NumPy-
style docstring parsers only recognize the bare section names (Notes,
Parameters, etc.); the parenthetical version confused the field-list
parser which then unindented the prior Parameters list incorrectly.

Move the Conley-rejection paragraph into the canonical Notes section
that already existed lower in the docstring, prefixed with a bold
"**Conley spatial-HAC rejection.**" lead-in so the content remains
visually distinguished. No content lost. Verified clean locally with
`python -m sphinx -W -q -b html docs /tmp/sphinx-html` (exit 0).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: igerber

diff_diff/synthetic_did.py

@@ -86,19 +86,6 @@ class SyntheticDiD(DifferenceInDifferences):
         Random seed for reproducibility. If None (default), results
         will vary between runs.
 
-    Notes (Conley spatial-HAC rejection)
-    ------------------------------------
-    SyntheticDiD does not support the Conley (1999) spatial-HAC analytical
-    sandwich. Passing ``vcov_type="conley"`` or any non-``None`` Conley
-    keyword (``conley_coords``, ``conley_cutoff_km``, ``conley_metric``,
-    ``conley_kernel``) to ``__init__`` or ``set_params`` raises
-    ``TypeError``. Rationale: SyntheticDiD's variance is derived from
-    bootstrap / jackknife / placebo resampling (Arkhangelsky et al. 2021
-    Algorithms 2–4), not the sandwich identity Conley plugs into. Adding
-    Conley support would require either an analytical SDID sandwich path
-    or a spatial-block bootstrap (Politis-Romano 1994 territory). Tracked
-    as a follow-up in ``TODO.md``.
-
     Attributes
     ----------
     results_ : SyntheticDiDResults
@@ -159,6 +146,18 @@ class SyntheticDiD(DifferenceInDifferences):
     - Standard DiD (uniform weights): ω_j = 1/N_control
     - Synthetic Control (exact matching): concentrated weights
 
+    **Conley spatial-HAC rejection.** SyntheticDiD does not support the
+    Conley (1999) spatial-HAC analytical sandwich. Passing
+    ``vcov_type="conley"`` or any non-``None`` Conley keyword
+    (``conley_coords``, ``conley_cutoff_km``, ``conley_metric``,
+    ``conley_kernel``) to ``__init__`` or ``set_params`` raises
+    ``TypeError``. Rationale: SyntheticDiD's variance is derived from
+    bootstrap / jackknife / placebo resampling (Arkhangelsky et al. 2021
+    Algorithms 2–4), not the sandwich identity Conley plugs into. Adding
+    Conley support would require either an analytical SDID sandwich path
+    or a spatial-block bootstrap (Politis-Romano 1994 territory). Tracked
+    as a follow-up in ``TODO.md``.
+
     References
     ----------
     Arkhangelsky, D., Athey, S., Hirshberg, D. A., Imbens, G. W., & Wager, S.