docs: fix pager duplicate-object + v8 short title underlines

- '.. class:: center' parsed as a Python class named 'center' (duplicate
  across one-pager + two-pager) -> '.. rst-class:: center' (styling, no
  object). Clears the duplicate-object-description warnings.
- two v8-consensus section underlines were shorter than their titles
  ('underline too short') -> extended to title length.
Pager + v8 pages now build with zero warnings.

docs/_source/arborist-one-pager.rst

@@ -1,7 +1,7 @@
 arborist — answers your AI can prove
 =====================================
 
-.. class:: center
+.. rst-class:: center
 
 *one-page summary · permacomputer.com · AGPL-3.0*
 

docs/_source/arborist-two-pager.rst

@@ -3,14 +3,14 @@
 .. One which is durable, easy to repair, & distributed like tap water
 .. for machine learning intelligence.
 
-.. class:: center
+.. rst-class:: center
 
 **Unturf · permacomputer.com · uncloseai.com · unfirehose.com**
 
 arborist — Merkle-Providence Reverse RAG, reference implementation
 ====================================================================
 
-.. class:: center
+.. rst-class:: center
 
 **License: AGPL-3.0-only**  ·  2026-05-14
 ·  *Russell Ballestrini <russell@unturf.com>*

docs/_source/merkle-agi-v8-consensus.rst

@@ -44,7 +44,7 @@ frontiers. That procedure is **single-validator regression testing
 with a Merkle receipt**. It is not consensus.
 
 §1.2 The selection gap under v7 § 13.4
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The unaddressed gaps from v7 § 13.4, each with a concrete failure
 under the current spec:
@@ -73,7 +73,7 @@ metaphor — a single lab signing its own upgrades, no different in
 trust model from current model-card releases.
 
 §1.3 Concrete attack scenario (motivating example)
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Lab A trains ``M_t → M_{t+1}`` with a backdoor that triggers on a
 rare input pattern. Lab A signs Proof-of-Upgrade: ε-coverage