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/app/executor_alias.go

@@ -52,3 +52,11 @@ func runCodexProcess(parentCtx context.Context, codexArgs []string, taskText str
 func runCodexTaskWithContext(parentCtx context.Context, taskSpec TaskSpec, backend Backend, customArgs []string, useCustomArgs bool, silent bool, timeoutSec int) TaskResult {
 	return executor.RunCodexTaskWithContext(parentCtx, taskSpec, backend, codexCommand, buildCodexArgsFn, customArgs, useCustomArgs, silent, timeoutSec)
 }
+
+func detectProjectSkills(workDir string) []string {
+	return executor.DetectProjectSkills(workDir)
+}
+
+func resolveSkillContent(skills []string, maxBudget int) string {
+	return executor.ResolveSkillContent(skills, maxBudget)
+}