Fix three critical UX issues in opal-task

Issue 1: Fix recurrence calculation for overdue tasks
- Use completion date (End) as base for next instance, not original due date
- If task due Monday completed Wednesday, next is Wednesday+7d not Monday+7d
- Fallback to Due date if End is not set
- Update test to verify new behavior

Issue 2: Fix description parsing to work without quotes
- Add parseAddArgs() to extract description from non-modifier words
- Description = all words that don't start with +, -, or contain :
- Enables: opal add buy groceries +shop carrots → 'buy groceries carrots'
- Validate description is required (error if only modifiers)
- Validate recurring tasks require due date

Issue 3: Implement flexible command syntax
- Add preprocessArgs() to parse arguments before Cobra routing
- Detect command position and split filters (left) from modifiers (right)
- Rewrite os.Args so Cobra routes correctly
- Enable both 'opal 2 done' and 'opal done 2' syntax
- Commands without modifiers accept filters on either side
- Commands with modifiers enforce [filters] command [modifiers]
- Add confirmation for modify without filters (modifies all tasks)

All commands updated to use preprocessed ParsedArgs from context.
All tests passing (33 tests).

opal-task/cmd/root.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"context"
 	"fmt"
 	"os"
 
@@ -8,14 +9,38 @@ import (
 	"github.com/spf13/cobra"
 )
 
+// ParsedArgs represents preprocessed command arguments
+type ParsedArgs struct {
+	Command   string
+	Filters   []string
+	Modifiers []string
+}
+
+// Context key for parsed args
+type contextKey string
+
+const parsedArgsKey contextKey = "parsedArgs"
+
+// Command classification
+var commandNames = []string{
+	"add", "list", "done", "modify", "delete",
+	"start", "stop", "count", "projects", "tags",
+}
+
+var commandsWithModifiers = map[string]bool{
+	"add":    true,
+	"modify": true,
+}
+
 var rootCmd = &cobra.Command{
 	Use:   "opal",
 	Short: "Opal task manager - taskwarrior-inspired CLI task management",
 	Long: `Opal is a powerful command-line task manager inspired by taskwarrior.
 It supports filtering, tags, priorities, projects, and recurring tasks.`,
 	Run: func(cmd *cobra.Command, args []string) {
-		// Default behavior: show pending tasks
-		if err := listTasks(args); err != nil {
+		// Default behavior: list tasks
+		parsed := getParsedArgs(cmd)
+		if err := listTasks(parsed.Filters); err != nil {
 			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 			os.Exit(1)
 		}
@@ -23,9 +48,103 @@ It supports filtering, tags, priorities, projects, and recurring tasks.`,
 }
 
 func Execute() error {
+	// Preprocess arguments BEFORE Cobra routing
+	if len(os.Args) > 1 {
+		parsed := preprocessArgs(os.Args[1:])
+
+		// Store in context for commands to use
+		ctx := context.WithValue(context.Background(), parsedArgsKey, parsed)
+		rootCmd.SetContext(ctx)
+
+		// Rewrite os.Args for Cobra based on parsed command
+		// This allows Cobra to route to the correct command
+		if parsed.Command != "list" || len(parsed.Filters) > 0 || len(parsed.Modifiers) > 0 {
+			// Reconstruct args: [command, ...filters, ...modifiers]
+			newArgs := []string{os.Args[0], parsed.Command}
+			newArgs = append(newArgs, parsed.Filters...)
+			newArgs = append(newArgs, parsed.Modifiers...)
+			os.Args = newArgs
+		}
+	}
+
 	return rootCmd.Execute()
 }
 
+// getParsedArgs retrieves preprocessed args from context
+func getParsedArgs(cmd *cobra.Command) *ParsedArgs {
+	if v := cmd.Context().Value(parsedArgsKey); v != nil {
+		if parsed, ok := v.(*ParsedArgs); ok {
+			return parsed
+		}
+	}
+	return &ParsedArgs{}
+}
+
+// preprocessArgs parses command-line arguments before Cobra routing
+// Returns: command name, filters, modifiers
+func preprocessArgs(args []string) *ParsedArgs {
+	if len(args) == 0 {
+		return &ParsedArgs{
+			Command:   "list", // Default command
+			Filters:   []string{},
+			Modifiers: []string{},
+		}
+	}
+
+	// Find command position
+	cmdIdx := -1
+	cmdName := ""
+
+	for i, arg := range args {
+		for _, name := range commandNames {
+			if arg == name {
+				cmdIdx = i
+				cmdName = name
+				break
+			}
+		}
+		if cmdIdx >= 0 {
+			break
+		}
+	}
+
+	// If no command found, treat as filters for default list command
+	if cmdIdx == -1 {
+		return &ParsedArgs{
+			Command:   "list",
+			Filters:   args,
+			Modifiers: []string{},
+		}
+	}
+
+	// Split arguments around command
+	leftArgs := args[:cmdIdx] // Everything before command
+	rightArgs := []string{}
+	if cmdIdx+1 < len(args) {
+		rightArgs = args[cmdIdx+1:] // Everything after command
+	}
+
+	// Determine how to interpret right args
+	if commandsWithModifiers[cmdName] {
+		// Command accepts modifiers
+		// Left = filters, Right = modifiers
+		return &ParsedArgs{
+			Command:   cmdName,
+			Filters:   leftArgs,
+			Modifiers: rightArgs,
+		}
+	} else {
+		// Command doesn't accept modifiers
+		// Both left and right are filters
+		allFilters := append(leftArgs, rightArgs...)
+		return &ParsedArgs{
+			Command:   cmdName,
+			Filters:   allFilters,
+			Modifiers: []string{},
+		}
+	}
+}
+
 func init() {
 	cobra.OnInitialize(initializeApp)