Exclude local credentials, private data, and generated artifacts

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

.gitignore

@@ -0,0 +1,31 @@
+node_modules/
+dist/
+.env
+*.local
+*.log
+.DS_Store
+
+# Runtime data — never commit
+data/
+backend/data/
+backend/dist/
+backend/node_modules/
+
+cshare-app/dist/
+cshare-app/node_modules/
+
+# Tool-specific configs
+.antigravitycli/
+
+# Live credentials and local runtime state
+.env.*
+!.env.example
+*.pem
+*.key
+*.pfx
+*.session*
+*.db*
+*.sqlite*
+.agents/
+.codex/
+.claude/