chore: allow PR authors to set topic labels via comments

This adds all topic labels (t-*) to the comment-to-label workflow,
allowing PR authors to manually add or remove topic labels by
commenting on their PRs. This is useful when the auto-labeling
from the diff is incorrect or incomplete.

Authors can now comment with lines like:
- `t-algebra` to add the label
- `-t-algebra` to remove the label

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: kim-em

.github/workflows/labels_from_comment.yml

@@ -25,7 +25,7 @@ jobs:
     steps:
     - name: Add / remove label based on comment
       run: |
-        labelArray=("awaiting-author" "WIP" "easy" "brownian" "carleson" "CFT" "FLT" "sphere-packing" "toric")
+        labelArray=("awaiting-author" "WIP" "easy" "brownian" "carleson" "CFT" "FLT" "sphere-packing" "toric" "t-algebra" "t-algebraic-geometry" "t-algebraic-topology" "t-analysis" "t-category-theory" "t-combinatorics" "t-computability" "t-condensed" "t-convex-geometry" "t-data" "t-differential-geometry" "t-dynamics" "t-euclidean-geometry" "t-geometric-group-theory" "t-group-theory" "t-linter" "t-logic" "t-measure-probability" "t-meta" "t-number-theory" "t-order" "t-ring-theory" "t-set-theory" "t-topology")
 
         # we strip `\r` since line endings from GitHub contain this character
         COMMENT="${COMMENT//$'\r'/}"