feat(displacement): internal displacement by region (IOM DTM, then IDMC events) #9014

Track internal displacement below the country level, not only UNHCR's yearly country totals.

Step 1: IOM DTM (shipped in #9015; fix #9130)

• Seed IOM DTM API v3 admin-1 rows daily (DTM_API_KEY is set on seed-bundle-health), keeping each operation's latest round.
• Serve them via GetInternalDisplacement, draw IDP bubbles and region-to-region routes on the displacement layer, and add an Internal tab to the UNHCR panel.
• /api/health probe dtmDisplacement uses an activation marker (seed-activated:displacement:dtm) until the first publish.

Step 2: IDMC event data (via HDX; seeder #9444, serving #9466, signals #9470, all merged)

• feat(displacement): show IDMC events on the map and panel, and in MCP (#9014) #9466: map points on the displacement layer, a Recent tab in the panel, and get_displacement_data view: "events" in MCP. The browser reads on-demand bootstrap key idmcIduDisplacement. No REST endpoint yet: public/openapi.json has no room (3 bytes left); it needs a budget recovery first.
• IDMC enters figures a median of 23 days after the displacement (p90 65), so "same-week" is not achievable: feat(displacement): seed IDMC internal displacement events from HDX (#9014) #9444 flags surges on a 30-day window vs the prior 150 days and adds newlyReported7d by publication date.
• Source: IDMC's own per-country IDU event CSVs on HDX — 116 datasets named <iso3>-idmc-idu-events under organisation international-displacement-monitoring-centre-idmc. No key needed. Discover them with CKAN package_search (fq=organization:international-displacement-monitoring-centre-idmc); all ~116 files (~36 MB) are re-read daily, ~29 s.
• Columns follow the Helix IDU schema: id, iso3, latitude, longitude, displacement_type (Conflict/Disaster), figure, displacement_date, event_id, event_name, category/type, sources, locations_*, description.
• The files include events older than 180 days (the AFG file starts 2025-02-27), so the seeder filters to the last 180 days by displacement_date itself.
• Seed daily for same-week surge detection, with seed-meta and a health key. Credit IDMC.
• Licence: HDX lists these as CC BY-IGO, but IDMC's API page says CC BY-NC-SA 3.0 IGO. IDMC confirmed by phone on 2026-10-20 that WorldMonitor may use the data; a confirming email is pending.
• The Helix API client_id (requested from ch.datainfo@idmc.ch on 2026-10-07 and chased on 2026-10-16) is no longer a blocker. If it arrives, one idus/last-180-days call can replace the ~116 per-country downloads.

Follow-ups

• REST endpoint for IDMC events after an OpenAPI budget recovery (about 3.2 KB).
• IDMC surges feed the cross-source signal feed as displacement-surge signals (feat(signals): emit IDMC internal displacement surges as cross-source signals (#9014) #9470, top five). The country instability index was left unchanged: no current surge is a Tier-1 country and IDMC lags by weeks; revisit if a Tier-1 country surges.
• Global cross-border arrivals and surge tracking: feat(displacement): global cross-border arrivals and surge tracking #9023.
• DTM in MCP: get_displacement_data view: "regions" (feat(mcp): serve IOM DTM regions from get_displacement_data (#9014) #9487, open).
• The SVG (mobile) map has never drawn the displacement layer; this predates DTM.