MUL-4971: Fix sub-issue attention escalation (ZIC-99)

[vicksiyi]

What does this PR do?

Fixes a stall in sub-issue orchestration where child issues entering in_review or blocked only produced ordinary status-change notifications. Parent coordinators could miss those states unless they were subscribed to the child/parent issue.

This adds a parent-level handoff for child review/block states, reusing the existing child-complete routing model: a system comment is posted on the parent, agent/squad parent assignees are woken through the existing deduped task path, and member parent assignees receive an action-required inbox item pointing at the child.

Related Issue

Closes #5464

Multica issue: ZIC-99

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Refactor / code improvement (no behavior change)
• Tests (adding or improving test coverage)
• CI / infrastructure

Changes Made

• Added child in_review / blocked parent handoffs in server/internal/handler/issue_child_done.go.
• Wired single issue and batch issue status updates to emit those handoffs.
• Added tests for agent parent wakeups, member parent inbox escalation, and batch deduplication.

How to Test

1. cd server
2. go test ./internal/handler -run 'TestChildAttention|TestBatchChildAttention|TestChildDone|TestBatchChildDone'
3. go test ./internal/handler

Note: make check-worktree exited 0 locally, but its PostgreSQL check printed that Docker was unavailable at /Users/icezero/.docker/run/docker.sock, so the meaningful local validation is the Go handler test suite above.

Checklist

• I have included a thinking path that traces from project context to this change
• I have run tests locally and they pass
• I have added or updated tests where applicable
• If this change affects the UI, I have included before/after screenshots
• I have updated relevant documentation to reflect my changes
• If I added a new runtime / coding tool / UI tab, I synced the change to landing copy (apps/web/features/landing/i18n/) and relevant docs (apps/docs/content/docs/)
• If this PR touches Chinese product copy, I checked it against apps/docs/content/docs/developers/conventions.zh.mdx (terminology, mixed-rule for task / issue / skill)
• I have considered and documented any risks above
• I will address all reviewer comments before requesting merge

AI Disclosure

AI tool used: Multica Agent

Prompt / approach:
Investigated GitHub #5464 and the existing child-done parent handoff path, then added the smallest backend change to surface child review/block states without changing terminal stage-barrier behavior.

Screenshots (optional)

N/A

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