Fix substring bug in dependency tree cycle detection (#159)

* Add .worktrees/ to .gitignore

Prevents git worktree contents from being tracked in the repository.

* Fix substring bug in dependency tree cycle detection

The cycle detection in GetDependencyTree() was using a simple substring
match which incorrectly flagged valid nodes as cycles. For example,
"bd-1" would be blocked because "bd-10" contains "bd-1" as a substring.

This bug affects any beads project where issue IDs contain each other as
substrings (BD-1/BD-10, ISSUE-1/ISSUE-10, etc).

Changed from:
  AND t.path NOT LIKE '%' || i.id || '%'

To delimiter-aware checks that respect the → separator:
  AND t.path != i.id
  AND t.path NOT LIKE i.id || '→%'
  AND t.path NOT LIKE '%→' || i.id || '→%'
  AND t.path NOT LIKE '%→' || i.id

This ensures we only match complete issue IDs, not substrings.

Added TestGetDependencyTree_SubstringBug to demonstrate and prevent
regression of this issue. The test creates a chain from bd-10 to bd-1
and verifies all nodes appear in the dependency tree.

Discovered while testing dependency tree visualization with bd-1/bd-10.

internal/storage/sqlite/dependencies.go

@@ -496,7 +496,10 @@ func (s *SQLiteStorage) GetDependencyTree(ctx context.Context, issueID string, m
 			JOIN dependencies d ON i.id = d.depends_on_id
 			JOIN tree t ON d.issue_id = t.id
 			WHERE t.depth < ?
-			AND t.path NOT LIKE '%' || i.id || '%'
+			AND t.path != i.id
+			AND t.path NOT LIKE i.id || '→%'
+			AND t.path NOT LIKE '%→' || i.id || '→%'
+			AND t.path NOT LIKE '%→' || i.id
 			)
 			SELECT id, title, status, priority, description, design,
 			acceptance_criteria, notes, issue_type, assignee,