cleanup: update .gitignore, sanitize .env.example, remove stale files

- Expanded .gitignore: miku-app/, dashboard/, .continue/, *.code-workspace,
  cheshire-cat artifacts (venv, benchmarks, test output), jinja templates
- Sanitized .env.example: replaced real webhook URL and user ID with placeholders
- Removed SECRETS_CONFIGURED.md (contained sensitive token info)
- Removed bot/static/system.html.bak (stale backup)
- Removed bot/utils/voice_receiver.py.old (superseded)

.gitignore

@@ -77,3 +77,24 @@ temp_*
 backups/
 *.bak
 *.backup
+
+# WIP / experimental subprojects
+miku-app/
+
+# Abandoned directories
+dashboard/
+
+# IDE / editor workspace files
+*.code-workspace
+.continue/
+
+# Cheshire Cat local artifacts
+cheshire-cat/venv/
+cheshire-cat/benchmark_results_*.json
+cheshire-cat/streaming_benchmark_*.json
+cheshire-cat/test_*_output.txt
+cheshire-cat/test_*_final.txt
+cheshire-cat/extracted_facts.json
+
+# Jinja templates (referenced by llama-swap config, not source)
+llama31_notool_template.jinja