docs: open ticket #000022 (adapter LossReport) + federation doc-discoverability fix

Both items surfaced by the 2026-05-07 arborist-vs-donto comparison
report (/home/fox/Downloads/arborist_vs_donto.pdf).

Ticket #000022 — adapter LossReport (PRD I9 analogue). Today wikitext
to_base() and html_page _normalize_text drop <ref> tags, image/category
wikilinks, HTML chrome, whitespace runs without recording any of it;
only the canonicalization-version pin survives. Ticket proposes a
sidecar adapter_loss_reports table (Option A) over Merkle-bound
loss_root (B) or audit-chain entries (C), preserving arborist's
"soft signals are sidecars" discipline. ~1.6% storage tax expected,
matching concept_relations. Doc-only; no code in this commit.

Federation doc-discoverability: PDF author concluded "federation
exists in code but the public docs page returned 404" because the
mesh page lives at /api/mesh.html and the concepts orientation
never surfaces the topic. Adds a "Federation across peers" section
to concepts.rst pointing at api/mesh, a :ref:\`federation\` anchor
+ context lead on api/mesh.rst, and a footer link in concepts.rst's
"Where to go next." Sphinx build passes; api/mesh.html#federation
deep link resolves.

docs/_source/api/mesh.rst

@@ -1,7 +1,13 @@
+.. _federation:
+
 Federation: multiplayer arborist
 ================================
 
-Gossip-based mesh for cross-peer data sharing.
+Gossip-based mesh for cross-peer data sharing. Arborist peers
+that ingest the same source under the same chunker and
+canonicalization compute bit-identical ``document_root`` hashes;
+the mesh layer is what lets peers exchange and verify each other's
+records without a central authority.
 
 .. automodule:: arborist.mesh
    :members: