Initial commit: Cyrene Plugins SDK + Plugin Manager

Extracted from Cyrene main repo (backend/pkg/plugins + backend/plugin-manager).
Contains SDK interfaces (Plugin/Tool/HostAPI), 13 built-in plugins,
ToolRegistry with call log ring buffer, and Plugin Manager REST API service.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,38 @@
+# cyrene-plugins
+# Community plugin SDK and plugin-manager service for Cyrene AI
+
+# Binaries
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+/plugin-manager
+/plugin-manager.exe
+
+# Test binary
+*.test
+
+# Output of go test
+*.out
+
+# Dependencies
+vendor/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Environment
+.env
+.env.local
+
+# Data
+data/