docs: fix citation slug bug (C1) (#38)

## Summary

Same init-substitution bug as the workbench (fixed there in its sibling
PR): `docs/attribution/CITATIONS.adoc`'s BibTeX key contained a space
(`@software{Trope Checker_2026,` — invalid) and every citation URL
pointed at the nonexistent `github.com/hyperpolymath/Trope Checker`.
Keys and URLs now use the real slug; prose titles unchanged.

## Changes

- BibTeX key → `trope_checker_2026`; all URL occurrences →
`github.com/hyperpolymath/trope-checker`

## RSR Quality Checklist

### Required

- [x] Tests pass — grep confirms zero remaining un-slugged URLs
- [x] Code is formatted — N/A (prose)
- [x] Linter is clean
- [x] No banned language patterns
- [x] No `unsafe` blocks / banned functions — N/A
- [x] SPDX headers present (unchanged)
- [x] No secrets included

## Testing

`grep -c "hyperpolymath/Trope Checker"` → 0.

## Screenshots

N/A.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01LPhj2Tjx4NUi8uTTsNbeJ1

---
_Generated by [Claude
Code](https://claude.ai/code/session_01LPhj2Tjx4NUi8uTTsNbeJ1)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

docs/attribution/CITATIONS.adoc

@@ -7,30 +7,30 @@
 
 [source,bibtex]
 ----
-@software{Trope Checker_2026,
+@software{trope_checker_2026,
   author = {Jewell, Jonathan D.A.},
   title = {Trope Checker},
   year = {2026},
-  url = {https://github.com/hyperpolymath/Trope Checker},
+  url = {https://github.com/hyperpolymath/trope-checker},
   license = {MPL-2.0}
 }
 ----
 
 == Harvard Style
 
-Jewell, J. (2026) _Trope Checker_ [Computer software]. Available at: https://github.com/hyperpolymath/Trope Checker
+Jewell, J. (2026) _Trope Checker_ [Computer software]. Available at: https://github.com/hyperpolymath/trope-checker
 
 == OSCOLA
 
-Jonathan D.A. Jewell, 'Trope Checker' (2026) <https://github.com/hyperpolymath/Trope Checker>
+Jonathan D.A. Jewell, 'Trope Checker' (2026) <https://github.com/hyperpolymath/trope-checker>
 
 == MLA
 
-Jewell, Jonathan D.A. "Trope Checker." 2026, github.com/hyperpolymath/Trope Checker.
+Jewell, Jonathan D.A. "Trope Checker." 2026, github.com/hyperpolymath/trope-checker.
 
 == APA 7
 
-Jewell, J. (2026). _Trope Checker_ [Computer software]. GitHub. https://github.com/hyperpolymath/Trope Checker
+Jewell, J. (2026). _Trope Checker_ [Computer software]. GitHub. https://github.com/hyperpolymath/trope-checker
 
 == See Also