fix(bmad-prd): utf-8 encoding on render script, correct workflow-map outputs

- render-validation-html.py reads findings/template and writes HTML/MD with
  explicit utf-8 encoding so non-ASCII content (smart quotes, em-dashes,
  non-English text under {document_output_language}) does not break on
  platforms whose default encoding is not utf-8.
- workflow-map.md 'Produces' column for bmad-prd now distinguishes
  Create/Update outputs from the Validate intent's validation-report
  artifacts.

docs/reference/workflow-map.md

@@ -46,7 +46,7 @@ Define what to build and for whom.
 
 | Workflow                | Purpose                                                                             | Produces                                          |
 |-------------------------|-------------------------------------------------------------------------------------|---------------------------------------------------|
-| `bmad-prd`              | Create, update, or validate a PRD — facilitated discovery, three intents in one skill | `prd.md`, `addendum.md`, `decision-log.md`        |
+| `bmad-prd`              | Create, update, or validate a PRD — facilitated discovery, three intents in one skill | Create/Update: `prd.md`, `addendum.md`, `decision-log.md`; Validate: `validation-report.html` + `.md` |
 | `bmad-create-ux-design` | Design user experience (when UX matters)                                            | `ux-spec.md`                                      |
 
 :::tip[Three intents in one skill]

src/bmm-skills/2-plan-workflows/bmad-prd/scripts/render-validation-html.py

@@ -220,7 +220,7 @@ def main(argv: list[str]) -> int:
     output_path = Path(args.output)
 
     try:
-        data = json.loads(findings_path.read_text())
+        data = json.loads(findings_path.read_text(encoding="utf-8"))
     except FileNotFoundError:
         print(f"error: findings file not found: {findings_path}", file=sys.stderr)
         return 1
@@ -228,7 +228,7 @@ def main(argv: list[str]) -> int:
         print(f"error: findings file is not valid JSON ({findings_path}): {e}", file=sys.stderr)
         return 1
     try:
-        template = template_path.read_text()
+        template = template_path.read_text(encoding="utf-8")
     except FileNotFoundError:
         print(f"error: template file not found: {template_path}", file=sys.stderr)
         return 1
@@ -268,10 +268,10 @@ def main(argv: list[str]) -> int:
     }
 
     rendered = string.Template(template).safe_substitute(substitutions)
-    output_path.write_text(rendered)
+    output_path.write_text(rendered, encoding="utf-8")
 
     md_path = output_path.with_suffix(".md")
-    md_path.write_text(render_markdown_report(data, findings, stats, grade))
+    md_path.write_text(render_markdown_report(data, findings, stats, grade), encoding="utf-8")
 
     print(json.dumps({
         "output": str(output_path),