fix(incident): fetch get by id through /incident/list-by-ids

[ysyneu]

Problem

flashduty incident get <id> [<id2>...] sent only incident_ids to POST /incident/list. That endpoint binds start_time / end_time as required, so every call failed:

Error: flashduty: EndTime is a required field, StartTime is a required field (code InvalidParameter, http 400)

The existing test stub answered every path with the same canned rows and never checked which endpoint was called, so the suite stayed green.

Fix

• get fetches through Incidents.ListByIDs (POST /incident/list-by-ids), which takes ids alone and returns the same incident row shape. Its help now uses the ListByIDs response description (top-level array, unchanged for jq '.[]' users).
• Short-id (num) resolution is unchanged: it still goes through /incident/list with its 30-day lookback.
• Tests assert the request path: short id → [/incident/list, /incident/list-by-ids]; full id → [/incident/list-by-ids] only. Both new assertions fail on the previous code.

Verification

• make check (fmt, lint, test -race, build): green. make gen-cards: no card diff.
• Against a live dev backend with the built binary:
  • incident get <full-id> --json → record with num, progress, detail_url
  • incident get <num> → resolves and returns the record
  • incident get <id1> <id2> <id3> → 3 rows (json and table)
  • The old wire shape (/incident/list with ids only) reproduces the 400 above on the same backend.

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