feat(web): dependencies between epics on the roadmap

Arrows from an epic to the ones that wait for it («bloquea» / «depende
de»), drawn over the bars; dashed red, plus a note in words, when one
starts before the epic blocking it ends. The next batch and the ideas
kept or dropped are written down in docs/10-futuro.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/lib/models/models.ts

@@ -71,6 +71,8 @@ export interface ChildProgress {
 export interface Epic {
   issue: IssueSummary;
   progress: ChildProgress;
+  /** Its relations: «bloquea» / «depende de» are the roadmap's arrows. */
+  links: IssueLink[];
 }
 
 /** What a saved view narrows the board to; empty: everything. */