fix: Minor issues #12 and #13 - ASCII mode and performance optimization

This commit addresses the remaining Minor issues from PR #94 code review:

Minor #12: Unicode Symbol Compatibility
- Added CODEAGENT_ASCII_MODE environment variable support
- When set to "true", uses ASCII symbols: PASS/WARN/FAIL
- Default behavior (unset or "false"): Unicode symbols ✓/⚠️/✗
- Updated help text to document the environment variable
- Added tests for both ASCII and Unicode modes

Implementation:
- executor.go:514: New getStatusSymbols() function
- executor.go:531: Dynamic symbol selection in generateFinalOutputWithMode
- main.go:34: useASCIIMode variable declaration
- main.go:495: Environment variable documentation in help
- executor_concurrent_test.go:292: Tests for ASCII mode
- main_integration_test.go:89: Parser updated for both symbol formats

Minor #13: Performance Optimization - Reduce Repeated String Operations
- Optimized Message parsing to split only once per task result
- Added *FromLines() variants of all extractor functions
- Original extract*() functions now wrap *FromLines() for compatibility
- Reduces memory allocations and CPU usage in parallel execution

Implementation:
- utils.go:300: extractCoverageFromLines()
- utils.go:390: extractFilesChangedFromLines()
- utils.go:455: extractTestResultsFromLines()
- utils.go:551: extractKeyOutputFromLines()
- main.go:255: Single split with reuse: lines := strings.Split(...)

Backward Compatibility:
- All original extract*() functions preserved
- Tests updated to handle both symbol formats
- No breaking changes to public API

Test Results:
- All tests pass: go test ./... (40.164s)
- ASCII mode verified: PASS/WARN/FAIL symbols display correctly
- Unicode mode verified: ✓/⚠️/✗ symbols remain default
- Performance: Single split per Message instead of 4+

Usage Examples:
  # Unicode mode (default)
  ./codeagent-wrapper --parallel < tasks.txt

  # ASCII mode (for terminals without Unicode support)
  CODEAGENT_ASCII_MODE=true ./codeagent-wrapper --parallel < tasks.txt

Benefits:
- Improved terminal compatibility across different environments
- Reduced memory allocations in parallel execution
- Better performance for large-scale parallel tasks
- User choice between Unicode aesthetics and ASCII compatibility

Related: #94

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/main_integration_test.go

@@ -87,16 +87,17 @@ func parseIntegrationOutput(t *testing.T, out string) integrationOutput {
 			}
 			inTaskResults = false
 		} else if inTaskResults && strings.HasPrefix(line, "### ") {
-			// New task: ### task-id ✓ 92% or ### task-id ✗ FAILED
+			// New task: ### task-id ✓ 92% or ### task-id PASS 92% (ASCII mode)
 			if currentTask != nil {
 				payload.Results = append(payload.Results, *currentTask)
 			}
 			currentTask = &TaskResult{}
 
 			taskLine := strings.TrimPrefix(line, "### ")
+			success, warning, failed := getStatusSymbols()
 			// Parse different formats
-			if strings.Contains(taskLine, " ✓") {
-				parts := strings.Split(taskLine, " ✓")
+			if strings.Contains(taskLine, " "+success) {
+				parts := strings.Split(taskLine, " "+success)
 				currentTask.TaskID = strings.TrimSpace(parts[0])
 				currentTask.ExitCode = 0
 				// Extract coverage if present
@@ -106,12 +107,12 @@ func parseIntegrationOutput(t *testing.T, out string) integrationOutput {
 						currentTask.Coverage = coveragePart
 					}
 				}
-			} else if strings.Contains(taskLine, " ⚠️") {
-				parts := strings.Split(taskLine, " ⚠️")
+			} else if strings.Contains(taskLine, " "+warning) {
+				parts := strings.Split(taskLine, " "+warning)
 				currentTask.TaskID = strings.TrimSpace(parts[0])
 				currentTask.ExitCode = 0
-			} else if strings.Contains(taskLine, " ✗") {
-				parts := strings.Split(taskLine, " ✗")
+			} else if strings.Contains(taskLine, " "+failed) {
+				parts := strings.Split(taskLine, " "+failed)
 				currentTask.TaskID = strings.TrimSpace(parts[0])
 				currentTask.ExitCode = 1
 			} else {