intake: put the backlog in the Recent feed

[Jammy2211]

Follow-up to #251. The feed held 50 and could only find 10, because it read every bucket except the largest: draft/ is 150 prompts against a handful of registry rows, so skipping it meant Recent saw almost none of what had been happening — and the paging added in #251 had nothing to page.

Drafts now carry their own date (PyAutoMind grows a Filed: prompt header) and the census reads it back, so a filed prompt is an event like any other.

On today's Mind the feed goes from 10 rows to a full 50 — 45 filed, 3 parked, 1 issued, 1 found — and the … reveal finally does something.

Details

• parse_header learns Filed:; backlog records carry a date.
• _header_date replaces the inline Issued: lookup and is shared by the backlog and in-flight legs. Issued: wins over Filed: when a prompt carries both — an issued prompt keeps the Filed: it had as a draft, and the later, more specific event is the one that dates the task.
• Epic members stay out, as they do in every pick list on the page: they are worked in order through their epic, and a Recent row hands out a standalone /start_dev.

Testing

• 4 new tests: a dated draft appears with the right event and payload, an undated one stays out, an epic member is never offered standalone, and Issued: beats Filed:.
• python3 -m pytest tests/ — 405 passed.
• Reveal driven in Chromium against the real regenerated dashboard: 10 → 20 → 30 → 40 → 50, button retires. Markdown page: 10 rows then 4 nested <details>, … 10 more (40 left) → (10 left).

Merge before the paired PyAutoMind PR (its refresh check renders using this repo's main).

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