feat(v0.5): include \$CTASK_ROOT/projects/ in SearchRoots by default

When CTASK_PROJECT_ROOT is unset, SearchRoots now appends
\$CTASK_ROOT/projects/ so that projects created under the default
category are discoverable from any shell without per-session env var
setup. Dedupe in scanAllRoots prevents double-counting workspaces that
are reachable both via the depth-2 scan under CTASK_ROOT and via the
new explicit search root. Adds a named regression test asserting no
duplicates appear in either ResolveQuery or ListWorkspaces results.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/config/config.go

@@ -60,21 +60,48 @@ func ResolveProjectRoot() string {
 }
 
 // SearchRoots returns the deduplicated list of workspace roots that all query
-// and listing operations must consult. Always includes CTASK_ROOT; also
-// includes CTASK_PROJECT_ROOT when set and different from CTASK_ROOT.
+// and listing operations must consult. Always includes CTASK_ROOT. When
+// CTASK_PROJECT_ROOT is set, adds that (unless it duplicates CTASK_ROOT).
+// When CTASK_PROJECT_ROOT is unset, adds $CTASK_ROOT/projects/ so that
+// projects created under the default category are discoverable from any
+// shell without per-session env var setup.
 func SearchRoots() []string {
 	taskRoot := ResolveRoot()
 	roots := []string{taskRoot}
+	seen := map[string]struct{}{searchRootKey(taskRoot): {}}
+
+	add := func(p string) {
+		if p == "" {
+			return
+		}
+		key := searchRootKey(p)
+		if _, dup := seen[key]; dup {
+			return
+		}
+		seen[key] = struct{}{}
+		roots = append(roots, p)
+	}
 
 	projRoot := ResolveProjectRoot()
-	if projRoot == "" {
-		return roots
+	if projRoot != "" {
+		add(projRoot)
+	} else {
+		// Default fallback: projects live under $CTASK_ROOT/projects/ when
+		// no override is set. Explicit search root makes discovery work
+		// from any shell.
+		add(filepath.Join(taskRoot, "projects"))
 	}
+	return roots
+}
 
-	if samePath(taskRoot, projRoot) {
-		return roots
+// searchRootKey returns the dedup key for a root path: cleaned, and
+// lower-cased on Windows for case-insensitive comparison.
+func searchRootKey(p string) string {
+	c := filepath.Clean(p)
+	if runtime.GOOS == "windows" {
+		return strings.ToLower(c)
 	}
-	return append(roots, projRoot)
+	return c
 }
 
 // samePath reports whether two absolute paths refer to the same directory