feat: add isolated proposal changesets

tests/fixtures/beta/.docforge/project.toml

@@ -11,6 +11,14 @@ authority_files = []
 cache_root = ".docforge/cache"
 index = ".docforge/cache/index.sqlite3"
 
+[changesets]
+root = ".docforge/changesets"
+
+[[changesets.writers]]
+id = "beta-editor"
+families = ["research"]
+operations = ["create", "update", "move", "delete"]
+
 [graph]
 allowed_relations = ["depends_on", "relates_to"]
 
@@ -21,6 +29,9 @@ max_query_chars = 200
 max_results = 20
 max_traversal_depth = 3
 max_context_tokens = 1000
+max_changesets = 10
+max_changeset_operations = 10
+max_changeset_bytes = 50000
 
 [[profiles]]
 id = "overview"