wip(resolver): collectors + unified predicate + tightened adapters [stdlib B, BLOCKED on 0106]

Collectors (resolver.zig: collectVisibleAuthors/collectNamespaceAuthors + AuthorSet
+ VisibilityMode, 4 unit tests) + unified visibility predicate + isNameVisible/
isCImportVisible adapters routed to flat modes. Tightening surfaces issue 0106
(stdlib comptime expansion relies on the over-permissive import_graph join), so
run_examples is 467/471 here. attempt-2 folds in the coupled comptime-context fix.

src/imports.zig

@@ -509,8 +509,9 @@ pub const NamespaceEdges = std.StringHashMap(std.StringHashMap(NamespaceTarget))
 
 /// The `RawDeclRef` a top-level node carries, or null when the node is not a
 /// selectable named declaration (e.g. `impl_block`, `var_decl`, `ufcs_alias`,
-/// a flat `c_import_decl`).
-fn rawDeclRefOf(decl: *const Node) ?RawDeclRef {
+/// a flat `c_import_decl`). Public so the unified resolver's namespace collector
+/// can classify a `NamespaceTarget.own_decls` node without re-deriving the map.
+pub fn rawDeclRefOf(decl: *const Node) ?RawDeclRef {
     return switch (decl.data) {
         .fn_decl => |*d| .{ .fn_decl = d },
         .const_decl => |*d| .{ .const_decl = d },