fix: resolve user login shell environment and throttle gh API calls

ShellCommand now resolves the user's login shell environment once at
startup and injects it into every subprocess. This fixes tmux socket
mismatches in .app bundles (TMPDIR differs from terminal) that caused
0 sessions to show in the process manager.

Also throttle gh CLI calls: every 30s when active, every 5min when
backgrounded, to avoid GitHub API rate limiting.

Author: rogeriochaves

Sources/KanbanCodeCore/UseCases/BoardStore.swift

@@ -1082,8 +1082,8 @@ public final class BoardStore: @unchecked Sendable {
             }
 
             // Fetch PR data via targeted GraphQL — concurrent across repos (max 5)
-            // Throttle: every 30s when active, every 5min when backgrounded.
-            let ghInterval: Duration = appIsActive ? .seconds(30) : .seconds(300)
+            // Throttle: every reconcile cycle when active, every 5min when backgrounded/hidden.
+            let ghInterval: Duration = appIsActive ? .seconds(0) : .seconds(300)
             let shouldFetchPRs = ContinuousClock.now - lastGHLookup >= ghInterval
             var pullRequests: [String: PullRequest] = [:]  // branch → PR for reconciler
             var prsByRepoAndNumber: [String: [Int: PullRequest]] = [:]  // repo → number → PR