Add self-hosted RCS backend, extension, and ops tooling

Ship the Go/SQLite API and Web UI, Chrome/Brave capture addon,
Docker Compose, Pangolin reverse-proxy support, and a user-crontab
watchdog so the binary stays running without systemd.

.gitignore

@@ -0,0 +1,25 @@
+# Data & binaries
+/data/*.db
+/data/*.db-journal
+/data/*.db-wal
+/data/*.db-shm
+/data/screenshots/*
+!/data/screenshots/.gitkeep
+/data/rcs.env
+/data/rcs.pid
+/data/rcs.log
+/data/rcs.watchdog.lock
+/backend/rcs
+/backend/bin/
+/bin/
+
+# Go
+vendor/
+
+# IDE / OS
+.idea/
+.vscode/
+*.swp
+.DS_Store
+.env
+.env.local