Add a SKILL and PROMPT for fixing a GitHub issue (#1558)

Signed-off-by: Cosmin Cojocar <cosmin@cojocar.ch>

.github/skills/gosec-fix-issue/SKILL.md

@@ -0,0 +1,49 @@
+---
+name: Fix Gosec Bug From Issue
+description: Analyze, reproduce, and fix a gosec bug reported in a GitHub issue with a confirmation-gated workflow.
+---
+
+# Fix a gosec bug from a GitHub issue
+
+Use this skill when you want to fix a bug described in a GitHub issue.
+
+## Required input
+
+Provide at least:
+
+- GitHub issue URL
+
+Optional but useful:
+
+- gosec version
+- Go version (`go version` output)
+- OS and environment details
+- extra reproduction notes
+
+## Execution workflow
+
+1. Review the GitHub issue thoroughly and extract the problem statement, reproduction hints, expected behavior, and actual behavior.
+2. Try to reproduce the issue against the current `master` version of gosec.
+3. Analyze the codebase and isolate the root cause.
+4. Produce a detailed, minimal fix plan and stop. Ask for confirmation before changing code.
+
+After confirmation, implement end-to-end:
+
+1. Keep the fix small and isolated to the issue scope.
+2. Follow good design principles and idiomatic Go.
+3. Add tests for both positive and negative cases.
+4. When a code sample is appropriate, add or update a sample in `testutils/` in the relevant rule sample file.
+5. Validate the result:
+   - Build succeeds
+   - Relevant tests pass
+   - `golangci-lint` has no warnings in changed code
+   - `gosec` CLI run on a sample confirms the issue is fixed
+
+## Output requirements
+
+- First response must only contain:
+  - Reproduction status on `master` (or clear blocker)
+  - Root cause analysis
+  - Detailed fix plan
+  - Confirmation request
+- Do not implement any code changes until confirmation is provided.