feat: migrate per-agent heartbeats to crons + forbid HEARTBEAT.md

[MarquisG]

Summary

OpenClaw's per-agent agents.list[].heartbeat does not fire for squad sub-agents today, so every recurring wake is now driven by a cron in crons/jobs.json — each squad's old HEARTBEAT.md procedure is embedded in a new heartbeat-pulse cron payload on the same 2h cadence, the heartbeat field is removed from agent.json (rejected as unknown), and HEARTBEAT.md is added to the validator's forbidden filenames. Validator + schema + 25 self-tests, docs (CLAUDE.md, README.md, bundle-reference.md, creating-a-squad.md, how-squads-work.md), and the create-squad / validate-squad skills are updated to match. Squad versions bumped: ai-seo-squad → 1.2.0, outreach-squad → 0.2.0, reddit-squad → 1.1.0.

Checklist

• node scripts/validate.mjs passes locally (CI runs it too).
• If a squad was added: the README.md official squad table is updated. (n/a — no new squads)
• If a squad was changed: its manifest.json version is bumped (semver).
• No <!-- TODO --> placeholders or template scaffolding left in a real squad bundle.

🤖 Generated with Claude Code

[getpancake]

🤖 Triage Assessment — P1 (High Priority)

Classification: Broken functionality fix, needs prompt review

This PR fixes a real runtime defect: agents.list[].heartbeat does not fire for squad sub-agents, meaning all existing squads (ai-seo, outreach, reddit) have non-functional heartbeats. The fix migrates heartbeat procedures into crons/jobs.json, removes the broken heartbeat field from agent.json, and adds validator enforcement of HEARTBEAT.md as a forbidden filename. 25 self-tests are included; squad versions are bumped correctly.

Rationale for P1: This fixes broken autonomous behavior across 3 production-ish squads. The validator and schema changes are well-tested, and the approach is clean. The PR has been open since May 26 and is unreviewed — that's too long for a fix to a systemic runtime issue.

Action items:

• Prioritize review — this has been open 13 days without a reviewer
• Confirm cron cadence matches old heartbeat cadence (2h)
• Deploy to test pod and verify cron fires correctly for at least one squad