docs: GST-976 re-audit, multi-label and lowercase Severity fields

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

changelog.d/gst-976-severity-field-first.md

@@ -2,4 +2,4 @@
 
 ### Fixed
 
-- When a reader's finding carries its own `Severity:` field, the collector uses that field. A word like "P0" in the finding's text (a plan phase name, for example) no longer makes it a blocker the reader marked `Blocks: no`. A label leading the line (`CRITICAL:`, `[P0]`, `- High:`, a label heading) still sets the floor, `Blocks: yes` still makes a finding CRITICAL, and the native voice's FIXABLE still collects as CRITICAL. Lines with no Severity field collect as before. (GST-976)
+- When a reader's finding carries its own `Severity:` field, the collector uses that field. A word like "P0" in the finding's text (a plan phase name, for example) no longer makes it a blocker the reader marked `Blocks: no`. A label leading the line (`CRITICAL:`, `[P0]`, `- High:`, a label heading) still sets the floor, `Blocks: yes` still makes a finding CRITICAL, and the native voice's FIXABLE still collects as CRITICAL. A field that names more than one label ("High/Critical") counts as no field, and a lowercase `severity:` keeps its label. Lines with no Severity field collect as before. (GST-976)

docs/review-policy.md

@@ -524,7 +524,7 @@ ones, and the arm lost blockers. `bin/gstack-review-dispatch` closes both ends:
    `merged.jsonl` with the label as written (a JSON line's `severity`, or the most
    severe of a prose line's Critical, High, Medium, Low, P0-P3, FIXABLE or INVESTIGATE
    wherever they stand, headings and table rows included, except that a line with its own `Severity` field takes that
-   field's label, so a severity word in the finding's text does not raise it, and a label leading the line stays its floor (GST-976); a top-level list item under a
+   field's label (any letter case; a field stating more than one label, "High/Critical", counts as none), so a severity word in the finding's text does not raise it, and a label leading the line stays its floor (GST-976); a top-level list item under a
    label-only heading takes the stronger of the two). A `Severity:` or `Blocks:` line
    continues the finding above it until a list item, heading, bold paragraph opener or a
    second line for the same field starts another: `Severity` sets its label (a label leading the finding stays its floor),