Align README agent/skill counts with onboarding docs (48 vs 53, 17 vs 19)

[PAMulligan]

Problem

The README states "48 Custom Agents" and "17 Development Skills", but the docs index further down (and docs/onboarding/architecture.md) reference "53 agents, 19 skills, 3 pipelines." They disagree.

Acceptance criteria

• Pick the correct counts (whichever is current truth on disk)
• Update README and docs/onboarding/architecture.md so they match
• Add a small CI check or pre-commit hook that recounts entries in .claude/agents/ and .claude/skills/ and flags drift

Notes

Low effort, high visibility — confuses first-time readers.