docs(skills): carve alerts out of the selectable-fields note

The alerts field appears in list/detail response shapes but no read
endpoint ever fills it; an incident's alerts come only from the
dedicated incident alerts command. Saying every response field is
selectable via --fields would invite --fields alerts and an
always-empty column.

Author: ysyneu

skills/flashduty/reference/incident.md

@@ -75,7 +75,7 @@ Projected `similar` lists stay below 16 KiB, and projected `detail --fields` out
 
 `comment` never accepts the text as a command-line argument — only `--comment-file <path>` (or `--comment-file -` to read stdin), so backticks/`$()`/quotes inside the comment are inert. The command also reads back every target's timeline after writing and exits non-zero unless it finds an entry matching what it sent, so `Commented on ...` is proof of content fidelity, not just acceptance — no separate manual read-back is needed. Leading and trailing whitespace is stripped before sending (the server strips it too, so this is what gets stored); everything else, including interior blank lines, is preserved exactly.
 
-> `incident list --output-format json|toon` defaults to the compact row projection `incident_id,title,incident_severity,progress,start_time,channel_id`. Pass `--fields incident_id,title,channel_id,start_time` when you need different list columns; use `incident detail <id>` / `incident get <id>` for full incident records. Any list-response field — including `labels` — is selectable this way (a key missing from the output means it wasn't selected, NOT that the server omits it; the command prints a stderr note when the default projection applies). Wide fields over many rows can exceed the 16 KiB structured-output bound and the command errors with "request fewer rows or fields" — lower `--limit`/page through, or use `insight` aggregates for distributions instead of dumping labels row by row.
+> `incident list --output-format json|toon` defaults to the compact row projection `incident_id,title,incident_severity,progress,start_time,channel_id`. Pass `--fields incident_id,title,channel_id,start_time` when you need different list columns; use `incident detail <id>` / `incident get <id>` for full incident records. Any list-response field — including `labels` — is selectable this way (a key missing from the output means it wasn't selected, NOT that the server omits it; the command prints a stderr note when the default projection applies). The one exception is `alerts`: neither list nor detail responses ever fill it — use `incident alerts <id>` for an incident's alerts. Wide fields over many rows can exceed the 16 KiB structured-output bound and the command errors with "request fewer rows or fields" — lower `--limit`/page through, or use `insight` aggregates for distributions instead of dumping labels row by row.
 
 ## Hot flow — full fault analysis (read-only summary)