chore: move .cognition/skills/ to .agents/skills/ (#474)

Rename the skills directory from the tool-specific `.cognition/`
path to the more generic `.agents/skills/` convention. Updates all
documentation references (AGENTS.md, dev/modules/, dev/design/) and
replaces Devin-specific attribution in debug-perlonjava skill with
tool-agnostic placeholders per AI_POLICY.md.

Generated with [Devin](https://cli.devin.ai/docs)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: fglock

.cognition/skills/debug-exiftool/SKILL.md .agents/skills/debug-exiftool/SKILL.md.cognition/skills/debug-exiftool/SKILL.md renamed to .agents/skills/debug-exiftool/SKILL.md

@@ -230,9 +230,9 @@ git add -A && git commit -m "Fix <what> by <how>
 
 <Details of the bug and fix>
 
-Generated with [Devin](https://cli.devin.ai/docs)
+Generated with [TOOL_NAME](TOOL_DOCS_URL)
 
-Co-Authored-By: Devin <noreply@cognition.ai>"
+Co-Authored-By: TOOL_NAME <TOOL_BOT_EMAIL>"
 ```
 
 ### 3. Push branch and create PR
@@ -247,7 +247,7 @@ gh pr create --title "Fix: description" --body "## Summary
 - [ ] Unit tests pass
 - [ ] Reproducer now works correctly
 
-Generated with [Devin](https://cli.devin.ai/docs)"
+Generated with [TOOL_NAME](TOOL_DOCS_URL)"
 ```
 
 ### 4. After PR is merged, clean up

…gnition/skills/debug-perlonjava/SKILL.md .agents/skills/debug-perlonjava/SKILL.md.cognition/skills/debug-perlonjava/SKILL.md renamed to .agents/skills/debug-perlonjava/SKILL.md .cognition/skills/debug-perlonjava/SKILL.md renamed to .agents/skills/debug-perlonjava/SKILL.md

@@ -188,7 +188,7 @@ The perl_test_runner.pl sets these automatically based on the test file being ru
 
 ## Available Skills
 
-See `.cognition/skills/` for specialized debugging and development skills:
+See `.agents/skills/` for specialized debugging and development skills:
 - `debug-perlonjava` - General debugging
 - `interpreter-parity` - JVM vs interpreter parity issues
 - `debug-exiftool` - ExifTool test debugging