feat(skills): add per-task skill spec auto-detection and injection

Replace external inject-spec.py hook with built-in zero-config skill
detection in codeagent-wrapper. The system auto-detects project type
from fingerprint files (go.mod, package.json, etc.), maps to installed
skills, and injects SKILL.md content directly into sub-agent prompts.

Key changes:
- Add DetectProjectSkills/ResolveSkillContent in executor/prompt.go
- Add Skills field to TaskSpec with parallel config parsing
- Add --skills CLI flag for explicit override
- Update /do SKILL.md Phase 4 with per-task skill examples
- Remove on-stop.py global hook (not needed)
- Replace inject-spec.py with no-op (detection now internal)
- Add 20 unit tests covering detection, resolution, budget, security

Security: path traversal protection via validSkillName regex,
16K char budget with tag overhead accounting, CRLF normalization.

Generated with SWE-Agent.ai

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

codeagent-wrapper/internal/executor/parallel_config.go

@@ -88,6 +88,13 @@ func ParseParallelConfig(data []byte) (*ParallelConfig, error) {
 						task.Dependencies = append(task.Dependencies, dep)
 					}
 				}
+			case "skills":
+				for _, s := range strings.Split(value, ",") {
+					s = strings.TrimSpace(s)
+					if s != "" {
+						task.Skills = append(task.Skills, s)
+					}
+				}
 			}
 		}
 
@@ -99,17 +106,17 @@ func ParseParallelConfig(data []byte) (*ParallelConfig, error) {
 			if strings.TrimSpace(task.Agent) == "" {
 				return nil, fmt.Errorf("task block #%d has empty agent field", taskIndex)
 			}
-				if err := config.ValidateAgentName(task.Agent); err != nil {
-					return nil, fmt.Errorf("task block #%d invalid agent name: %w", taskIndex, err)
-				}
-				backend, model, promptFile, reasoning, _, _, _, allowedTools, disallowedTools, err := config.ResolveAgentConfig(task.Agent)
-				if err != nil {
-					return nil, fmt.Errorf("task block #%d failed to resolve agent %q: %w", taskIndex, task.Agent, err)
-				}
-				if task.Backend == "" {
-					task.Backend = backend
-				}
-				if task.Model == "" {
+			if err := config.ValidateAgentName(task.Agent); err != nil {
+				return nil, fmt.Errorf("task block #%d invalid agent name: %w", taskIndex, err)
+			}
+			backend, model, promptFile, reasoning, _, _, _, allowedTools, disallowedTools, err := config.ResolveAgentConfig(task.Agent)
+			if err != nil {
+				return nil, fmt.Errorf("task block #%d failed to resolve agent %q: %w", taskIndex, task.Agent, err)
+			}
+			if task.Backend == "" {
+				task.Backend = backend
+			}
+			if task.Model == "" {
 				task.Model = model
 			}
 			if task.ReasoningEffort == "" {