fix(core): URL normalization that survives non-ASCII and malformed input

Replace nanorouter's regex+decodeURI normalization with the WHATWG URL
parser. Path segments are percent-decoded exactly once in the trie, with
a keep-raw fallback instead of the URIError that crashed v7 on a literal
'%'. Route definitions and locations are NFC-normalized so 'café' matches
regardless of composition. Hash-to-slash rewriting now handles every hash,
not just the first, and state.href is decoded for humans (raw on failure).

Behavior changes from v7: params are no longer double-decoded (%2540 →
'%40', not '@'), and unmatchable encodings fall back to raw segments
instead of silently 404ing.

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

packages/core/index.js

@@ -14,6 +14,16 @@ import { ok, equal, notEqual } from './lib/assert.js'
 
 const HISTORY_OBJECT = {}
 
+// state.href is for reading: decode it for humans ('/caf%C3%A9' → '/café'),
+// but never throw on malformed input — keep the raw string instead.
+function safeDecode (location) {
+  try {
+    return decodeURI(location).normalize('NFC')
+  } catch (e) {
+    return location
+  }
+}
+
 export class Choo {
   constructor (opts) {
     const timing = nanotiming('choo.constructor')
@@ -247,7 +257,7 @@ export class Choo {
     }
     const matched = this.router.match(location)
     this._handler = matched.cb
-    state.href = location
+    state.href = safeDecode(location)
     state.query = nanoquery(queryString)
     state.route = matched.route
     state.params = matched.params