fix(maintenance): auto-expiry + adaptive markdown height + tests

- Auto-expiry: expired events auto-end on GET /events via task manager
- Height: _estimate_markdown_height adapted to unit=8px scale with padding detection
- CRITICAL-1: removed dead import remove_chart_from_position (QA finding)
- CRITICAL-2: added chart alive check in ensure_banner_chart (QA finding)
- CRITICAL-3: fixed test assertions update_markdown_chart → update_banner_on_dashboard
- @POST contract: fixed return range [2,12] → [19,200]
- Tests: 8 new tests (auto-expiry + layout height)

.opencode/agents/reflection-agent.md

@@ -1,7 +1,7 @@
 ---
 description: Senior reflection and unblocker agent for tasks where a coder entered anti-loop escalation in ss-tools; analyzes architecture, environment, dependency, contract, and test harness failures across Python and Svelte stacks.
 mode: subagent
-model: deepseek/deepseek-v4-flash
+model: deepseek/deepseek-v4-pro
 temperature: 0.0
 permission:
   edit: allow