Add epic closure management commands (fixes #62)

- Add 'bd epic status' to show epic completion with child progress
- Add 'bd epic close-eligible' to bulk-close completed epics
- Add GetEpicsEligibleForClosure() storage method
- Update 'bd stats' to show count of epics ready to close
- Add EpicStatus type for tracking epic/child relationships
- Support --eligible-only, --dry-run, and --json flags
- Fix golangci-lint config version requirement

Addresses GitHub issue #62 - epics now have visibility and
management tools for closure when all children are complete.

Amp-Thread-ID: https://ampcode.com/threads/T-e8ac3f48-f0cf-4858-8e8f-aace2481c30d
Co-authored-by: Amp <amp@ampcode.com>

internal/types/types.go

@@ -183,13 +183,14 @@ type TreeNode struct {
 
 // Statistics provides aggregate metrics
 type Statistics struct {
-	TotalIssues      int     `json:"total_issues"`
-	OpenIssues       int     `json:"open_issues"`
-	InProgressIssues int     `json:"in_progress_issues"`
-	ClosedIssues     int     `json:"closed_issues"`
-	BlockedIssues    int     `json:"blocked_issues"`
-	ReadyIssues      int     `json:"ready_issues"`
-	AverageLeadTime  float64 `json:"average_lead_time_hours"`
+	TotalIssues              int     `json:"total_issues"`
+	OpenIssues               int     `json:"open_issues"`
+	InProgressIssues         int     `json:"in_progress_issues"`
+	ClosedIssues             int     `json:"closed_issues"`
+	BlockedIssues            int     `json:"blocked_issues"`
+	ReadyIssues              int     `json:"ready_issues"`
+	EpicsEligibleForClosure  int     `json:"epics_eligible_for_closure"`
+	AverageLeadTime          float64 `json:"average_lead_time_hours"`
 }
 
 // IssueFilter is used to filter issue queries
@@ -210,3 +211,11 @@ type WorkFilter struct {
 	Assignee *string
 	Limit    int
 }
+
+// EpicStatus represents an epic with its completion status
+type EpicStatus struct {
+	Epic            *Issue `json:"epic"`
+	TotalChildren   int    `json:"total_children"`
+	ClosedChildren  int    `json:"closed_children"`
+	EligibleForClose bool  `json:"eligible_for_close"`
+}