chore: keep ISSUE-*.md task notes local

The ISSUE-*.md files are local working notes, not repository content. They
stay on disk, are git-ignored and are no longer referenced from committed
files.

Changes:
- ISSUE-*.md: removed from the index (kept locally)
- .gitignore: ignore ISSUE-*.md
- AGENTS.md: local issues are git-ignored and never committed
- docs/arc42/11-risks-and-technical-debt.md: drop the ISSUE-*.md debt item

Tests: documentation and repository hygiene only; git check-ignore confirms
the files are ignored.

Author: kvs-coder

.gitignore

@@ -93,3 +93,6 @@ library/libs/*.aar
 
 # IDE state
 .idea/
+
+# Local task notes, not for the repository
+ISSUE-*.md

AGENTS.md

@@ -366,7 +366,7 @@ Refs: #<issue>
 * `Refs: #<issue>` is required whenever an issue exists.
 
 ### Local Issues
-Work not yet on GitHub lives in `ISSUE-<slug>.md` files at the repo root, titled with the Conventional Commit header the work will ship under. File one on GitHub with the `github-create` skill (or `gh issue create --body-file ISSUE-<slug>.md`), then delete the local file in the PR that references it.
+Work not yet on GitHub lives in `ISSUE-<slug>.md` files at the repo root, titled with the Conventional Commit header the work will ship under. They are for local use only: git-ignored, never committed or referenced from committed files. File one on GitHub with the `github-create` skill (or `gh issue create --body-file ISSUE-<slug>.md`) when it should become public.
 
 ---