feat(cron): convert heartbeat tasks: entries into independent cron jobs (#113165)

Each legacy heartbeat tasks: entry becomes an editable system-created cron
job (declaration key heartbeat-task:<agentId>:<hash>, per-occurrence
identity for duplicate names) that fires a guarded heartbeat wake carrying
the task prompt plus current monitor scratch context. Task cadence is now
independent of the base heartbeat interval; active-hours, busy-retry,
min-spacing, and flood guards are preserved, deferred payload-carrying
wakes are retained and retried after the spacing floor, and colliding
task/event wakes cannot starve each other.

openclaw doctor --fix migrates existing blocks: async parse/plan, then one
synchronous SQLite transaction that rereads the pinned scratch revision,
upserts job rows, and strips the tasks: block atomically — concurrent
doctors serialize on the database and a losing run aborts untouched.
Orphan fields, invalid intervals, and incomplete entries block migration
of their block with a clear finding instead of silent text loss. The
runtime tasks: parser is deleted; leftover text is ordinary scratch prose.

Nine Codex gpt-5.6-sol xhigh autoreview cycles; final verdict clean.

docs/docs_map.md

@@ -66,6 +66,7 @@ Do not edit it by hand; run `pnpm docs:map:gen`.
   - H2: Quick start
   - H2: How cron works
   - H2: Schedule types
+  - H3: Heartbeat task migration
   - H3: Stream sources
   - H3: Dynamic cadence (pacing)
   - H3: Day-of-month and day-of-week use OR logic
@@ -3602,7 +3603,7 @@ Do not edit it by hand; run `pnpm docs:map:gen`.
   - H3: Per-channel vs per-account examples
   - H3: Common patterns
   - H2: Monitor scratch (optional)
-  - H3: tasks: blocks
+  - H3: Schedule recurring checks with cron
   - H3: Can the agent update its scratch?
   - H2: Manual wake (on-demand)
   - H2: Cost awareness