Closes#1522
## Summary
- Call `history.replaceState` in `doTrace()` after the hash is
validated, so the URL becomes `#/tools/trace/<hash>` and can be shared
directly.
## Change
`public/traces.js` — one line added:
```js
history.replaceState(null, '', `#/tools/trace/${encodeURIComponent(hash)}`);
```
The read path (`init()` picks up the hash from the URL on load) already
existed — only the write path was missing.
