feat(html): adoption-style hydration with mismatch reporting

hydrate(oldNode, newNode) normalizes the client tree to parser text-node
granularity, walks both trees to report the first server/client markup
disagreement (node, text, attribute, or child count, with a path), then
morphs — matching nodes are adopted in place, the client render wins.
choo.mount() now hydrates and console.warns on mismatch.

Building this surfaced two real isomorphism divergences, both fixed:
adjacent text nodes from template holes vs the parser's merged runs
(folded via Node.normalize), and the server serializing onclick="" where
the browser sets a property — event handlers now leave no trace in server
markup at all.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd

packages/html/package.json

@@ -10,12 +10,14 @@
     },
     "./browser": "./browser.js",
     "./server": "./server.js",
+    "./hydrate": "./hydrate.js",
     "./raw": "./raw.js",
     "./morph": "./morph.js"
   },
   "files": [
     "browser.js",
     "server.js",
+    "hydrate.js",
     "raw.js",
     "morph.js"
   ],