refactor: ValueCleaner is the named choke point (H1)

The choke point moves out of AttrWriter into ValueCleaner (catalog, the
composition's VariableRef, sanitizer): clean() (was AttrWriter::cleanValue),
kindOf(), guardPath() and the private cleanNode/kind/unknownKind/tightens with
VALUE_KEY, URL_KEY, URL_SEGMENT, STRICTNESS, BUILDER_ONLY (its docblock now sits
on it; STRUCTURE stays in AttrWriter). Code of the pipeline moved unchanged.
- ValueCleaner's docblock is the one canonical description: steps 0-8 with their
  rulings in code order, invariants I1-I3; the step comments in cleanNode carry
  the same numbers. AttrWriter/ShortformWriter/Composer/TextReplacer docblocks
  point there and keep only their own rules.
- ValueCleaner::textReplacementFor($module) holds the D10 rule that was a
  closure in DiviReplaceTextAbility::replace (text/html only, clean() by kind).
- AttrWriter, ShortformWriter and Composer take the ValueCleaner; DiviComposition
  builds one per composition (cleaner()).
Tests: the eight AttrWriterTest methods that only exercised cleanValue/kindOf
moved verbatim to ValueCleanerTest (clean/kindOf, ComposeFixture::cleaner());
mixed tests call the cleaner in place; +1 test for textReplacementFor. Every
provider row and per-test assertion count unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/Divi/Pages/WpValueSanitizer.php

@@ -9,7 +9,7 @@ use LIT\MCP\Integrations\Divi\Compose\ValueSanitizer;
 /**
  * WordPress sanitizing of Divi values (spec §5.6/§10). Because DiviSaver bypasses kses for the
  * page as a whole (kses would re-serialize every untouched block, D7), every value this plugin
- * writes goes through here instead – always via AttrWriter::cleanValue(), which also checks
+ * writes goes through here instead – always via ValueCleaner::clean(), which also checks
  * $variable(…)$ references before and after these sanitizers.
  *
  * Rich text and code depend on unfiltered_html like in core (ruling S4): administrators keep