Add Healthcare SEO Metadata agent and validation script

[dariank38]

What this adds

New agent: agents/healthcare-seo-metadata.md (draft status)

Generates SEO metadata — page title, meta description, URL slug, and H1 — for healthcare web pages from pasted copy, a draft, or an outline. It complements the Healthcare Web Content agent by covering the metadata step before Sitecore publication:

• Deterministic numbered rules with hard character bounds (title <= 60 chars including the Kelsey-Seybold suffix, meta description 120-155) and self-reported character counts in the output.
• Uses the {PIPE} token convention for the vertical bar in title tags, converted to the literal character only at output time.
• Same accuracy guardrails as the content agent: no invented statistics or claims, no marketing superlatives, declines out-of-scope work.
• 4,528 chars of instruction text — well under the 8K Copilot Studio limit.

New script: scripts/validate.py

Run python scripts/validate.py to check every agent in agents/ for:

1. Instruction text <= 8,000 characters — counts only the ## Instructions section, which is what actually gets pasted into Copilot Studio. wc -c counts the whole file (frontmatter, Purpose section, organizational headings) and over-counts.
2. Literal | characters (should be {PIPE} — Copilot Studio strips/corrupts pipes).
3. Markdown tables (not rendered reliably by Copilot Studio).
4. Frontmatter completeness (name, description, platform, status, created, updated).

All four agents currently pass. CLAUDE.md is updated to point the post-edit check at the validator and document why it replaces wc -c.