fix(rwa-alpha): replace UTF-8 box-drawing chars with ASCII

[VibeCodeDaddy69]

Summary

• Replace box-drawing characters (└, ├, ┌, │, ─) in skill.md with ASCII equivalents (+--, |--, +, |, -)
• Replace Unicode arrow → with -> in both skill.md and SUMMARY.md
• Fix CI Phase 1 structure validation panic: the Rust linter crashes on multi-byte UTF-8 chars at non-char-boundary byte offsets (lint.rs:873)

Context

PR #287 was merged with box-drawing characters that cause the CI linter to panic. This follow-up fixes the encoding issue.

Test plan

• CI Phase 1 structure validation passes without panic
• skill.md renders correctly with ASCII tree/box chars
• All content preserved — only decorative characters changed

🤖 Generated with Claude Code

[github-actions]

✅ Phase 1: Structure Validation — PASSED

Linting skills/rwa-alpha...

  ⚠️  [W010] description is 285 chars (recommended < 200)
  ⚠️  [W140] SKILL.md references 3 external URL(s) not listed in api_calls: 'http://localhost:3249', 'http://localhost:3249', 'http://localhost:3249'. Add them to api_calls in plugin.yaml so reviewers can verify them.

✓ Plugin 'rwa-alpha' passed with 2 warning(s)

→ Proceeding to Phase 2: Build Verification