open the decision reader without re-contributing its tab

The decisions extension tore down and re-contributed the decisions.detail
context-panel tab on every selection, racing the view's own subscription and
leaving the panel unrevealed — so clicking a decision often did nothing. Match
the working ticket panel: contribute the tab once (static), and on selection
just reveal the context panel and activateTab; DecisionDetailView loads via its
existing subscription.

T-188.

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

CHANGELOG.md

@@ -18,6 +18,10 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Fixed
 
+- Clicking a decision opens it in the decision reader again — the decisions
+  extension no longer tears down and re-contributes its panel tab on every
+  selection; it activates a static tab and reveals the panel like the ticket
+  panel. (T-188)
 - Clicking a markdown file opens it in the right-side markdown reader again —
   the files panel, the Claude Config tab, and wiki `.md` links now publish to
   the reader instead of the editor. (T-187)