fix(dashboards): use date for charted time fields so time-series render

[os-zhuang]

Several dashboards' time-series charts and "last N months/days" KPIs silently rendered "No rows" even though the data existed.

Root cause (platform-level)

The analytics dataset executor binds dashboard date tokens ({12_months_ago}, {90_days_ago}, {today}, …) as ISO date strings ("2025-06-18").

• A Field.date column stores ISO text → col >= '2025-06-18' matches. ✅
• A Field.datetime column stores an integer epoch (1780012800000). In SQLite an INTEGER always sorts before any TEXT, so epoch >= 'YYYY-MM-DD' is always false → empty result. ❌

The un-filtered cube returns the rows (which is why the data looked present). Confirmed by diffing the working evidence KPI (expires_on = date → text storage) against the broken assessments chart (assessed_at = datetime → epoch storage), and by direct SQLite queries:

WHERE assessed_at >= '2025-06-18'   → 0 rows   (datetime/epoch column)
WHERE expires_on  >= '2026-06-18'   → 2 rows   (date/text column)

Template fix

Change the charted / date-token-filtered timestamp fields from datetime → date (day granularity is all these reports need; the column then stores ISO text the analytics layer compares correctly):

field	chart
compliance_assessment.assessed_at	Assessments by Month
todo_task.completed_at	Throughput by Week
expense_report.reimbursed_at	Spend by Month
content_piece.published_at	Published by Month
content_publication.published_at	ROI dashboard (90-day KPIs + charts)

Deliberately not changed: helpdesk_ticket.resolved_at stays datetime — SLA-resolution timing needs sub-day precision (flows compare it, breach logic uses it). Its "Resolutions by Day" chart stays empty until the platform binds epoch for datetime columns. The full gotcha is documented in AGENTS.md for future template authors.

Verification

• Fresh boot stores all five fields as ISO text (typeof = text).
• Chart SQL (status IN (...) AND assessed_at >= '2025-06-18') goes 0 → 4 rows.
• Browser: the compliance "按月完成的评估（近 12 个月）" chart now renders a line (y-axis populated) where it previously showed "No rows".

🤖 Generated with Claude Code