feat(taiga): Ticket verknüpfen — URL/Ref-Feld mit Betreff-Bestätigung (D91-Nachtrag 11)

Ein Knopf im Knoten-Fenster bindet ein bestehendes Taiga-Ticket an den
Knoten: Die eingefügte Ticket-URL trägt Slug, Typ und Nummer selbst; eine
nackte Nummer wird per Probe Story-dann-Task aufgelöst. Verknüpft wird erst
nach Anzeige des Betreffs; geschrieben werden Ref-Token und ggf.
&taiga.<slug> in einem Undo-Schritt, der geholte Stand füllt den
Ticket-Cache. Eine URL einer fremden Instanz wird benannt statt verknüpft.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CHANGELOG.md

@@ -19,6 +19,10 @@ reverse.
 
 ## 2026-08-28
 
+- "Link ticket" in the node window binds an existing Taiga story or task to a node: paste the ticket's URL — it carries project, type and number by itself — or enter a ref or bare number
+- A bare number is resolved by probing story then task, and the ticket's subject is shown before anything is written — you link what you saw
+- Linking appends the ref and, where needed, the `&taiga.slug` tag in one undo step, and pre-fills the ticket cache so window and divergence mark agree at once
+- A ticket URL from a different Taiga instance is named as such instead of silently linking a same-numbered ticket on yours
 - One bulk request reads the status of all referenced tickets: the proxy fans the refs out right next to the Taiga instance, so the cost scales with the refs in the plan — not with a project that holds thousands of tickets
 - With a Taiga login, diverging tickets show up in the diagram: a ref whose ticket status no longer matches the node's box turns amber — as its own little badge where the ref is the node id and thus not part of the title
 - The bulk result pre-fills the node window's ticket cache, so hovering a ticket node usually needs no request of its own any more