Add candidate to preview URL

[ai]

We do not keep the current selected candidate in /feeds/add URL.

Let’s add it. It will simplify the two-page logic a lot since we will not have route-less back logic.

• Add candidate to core/router.ts
• Add route to web/stores/router.ts
• Change core/preview.ts to use router
• Change web client to use links instead of buttons on Add Feed page

[ilyatitovich]

I want to take it

[ai]

Sure!