Add advisory for phases with 31-50 requirements (#10)

[Diyaaa-12]

What & why

Adds a soft advisory (not a hard fail) when a PRD phase has 31–50
requirements, nudging authors toward the recommended <= 30 per phase without
blocking the build. CHECK 5 in validate_prd.py still hard-fails above 50 as
before — only the 31–50 range now prints an ADVISORY line while keeping exit
code 0.

Also fixes a pre-existing cross-platform bug surfaced while testing on
Windows: validate_prd.py crashed with UnicodeEncodeError when printing
Korean PRD content to a Windows console (cp1252 default encoding). Added
sys.stdout.reconfigure(encoding="utf-8") / sys.stderr.reconfigure(...) at
the top of the script, and set encoding="utf-8" on the subprocess.run call
in the test helper so the test suite doesn't hit the same issue capturing
output on Windows.

Closes #10

Checks

• Ran the three local checks and they pass:
  • python3 skills/prd-maker/scripts/test_validate_prd.py
  • python3 .github/scripts/check_skill_structure.py
  • python3 .github/scripts/check_manifests.py
• Updated docs (README.md / README.ko.md) if usage or behavior changed — not touched; this only changes internal linter output, no user-facing usage change
• If I bumped the version, I bumped it in both .claude-plugin/plugin.json and .codex-plugin/plugin.json — no version bump made, not touched

Notes for reviewers

• No docs update needed — this only changes internal linter output
  (an advisory line), not the PRD template or user-facing CLI usage. Happy to
  add a note to README if you'd prefer it documented.
• check5_requirements_cap() now returns a 3-tuple (passed, detail, advisories) instead of 2. Updated the one caller in run_checks()
  accordingly — grep confirms no other callers.
• Flagging the Windows Unicode fix separately in case you'd rather split it
  into its own PR — it's unrelated to the advisory feature but I hit it while
  running the required local checks and didn't want to leave the linter
  broken on Windows.

[jcmaker]

Thanks for this — really solid work! 🙏 I ran everything locally and the feature itself is in great shape:

• ✅ All 19 unit tests pass (test_validate_prd.py)
• ✅ check_skill_structure.py and check_manifests.py both pass
• ✅ Verified the advisory end-to-end: a phase with 35 requirements keeps exit code 0, CHECK 5 still PASS, and the ADVISORY - Phase "..." has 35 requirements (recommended <= 30) line prints as intended. Nice touch keeping the hard-fail at >50 untouched.
• ✅ The Windows reconfigure(encoding="utf-8") fix is a sensible cross-platform improvement.

One small cleanup before merge 🧹 — in validate_prd.py the imports got duplicated during the patch:

import re
import sys
import re          # <- duplicate
import sys         # <- duplicate
from pathlib import Path
...
from pathlib import Path   # <- duplicate (line 31)

Could you collapse those down to a single import re, import sys, and one from pathlib import Path? It's harmless functionally, but let's keep the top of the file clean. (Tiny nit while you're in there: the two test classes lost their blank-line separation — class TestCheck5RequirementsCap and class TestAssumptions are now flush against the previous block; PEP 8 likes 2 blank lines between top-level classes.)

Once the imports are deduped I'll merge. Thanks again! 🚀

[Diyaaa-12]

Cleaned up — imports deduped (single import re, import sys, from pathlib import Path) and PEP 8 blank-line spacing fixed between TestCheck5RequirementsCap and TestAssumptions. All 19 tests still passing locally. Ready for another look whenever you get a chance 🙏