opencode-sandbox: OpenCode 2 in a sandbox for any project

Runs OpenCode 2 with full permissions while containing its mistakes:

- egress filter: squid in a container per project; squid.conf is rendered
  from layered egress.conf files (package, user, project, local) with
  allow/block/connect rules and expect-pass/expect-block self-tests
- netlock: nftables rejects direct egress for the opencode-sandbox group
  (installed once with sudo as a systemd unit)
- bubblewrap: read-only host, writable project, worktrees and state;
  credentials hidden; ssh keys via the host's ssh-agent; session bus
  replaced by an xdg-dbus-proxy limited to notifications; no permission
  prompts (sudo and systemd-run denied); refuses to run unsandboxed
- per-project state in ~/.local/share/opencode-sandbox/<name>
- worktrees: `wt add|rm|list` with project hooks
- skills mounted per project; the opencode-sandbox skill explains the
  environment to the agent
- plugins as submodules: context-panel, skill-compact-resurrect;
  global config adds opencode-notifier and cc-safety-net
- README in English and Russian

Makefile

@@ -0,0 +1,30 @@
+PREFIX ?= $(HOME)/.local
+BIN    := $(PREFIX)/bin/opencode-sandbox
+
+.PHONY: help install uninstall plugins lint
+
+help:
+	@echo "make install     link bin/opencode-sandbox into $(PREFIX)/bin and fetch plugins"
+	@echo "make uninstall   remove the link"
+	@echo "make plugins     fetch or update plugins (git submodules)"
+	@echo "make lint        bash -n and shellcheck"
+
+install: plugins
+	@mkdir -p $(dir $(BIN))
+	ln -sfn $(CURDIR)/bin/opencode-sandbox $(BIN)
+	@echo "✓ $(BIN) → $(CURDIR)/bin/opencode-sandbox"
+	@case ":$$PATH:" in *":$(PREFIX)/bin:"*) ;; *) echo "⚠ $(PREFIX)/bin is not in PATH";; esac
+
+uninstall:
+	rm -f $(BIN)
+
+plugins:
+	git submodule update --init --recursive
+
+lint:
+	@for f in bin/opencode-sandbox lib/*.sh egress/entrypoint.sh shim/xdg-open templates/project/hooks/*.example; do \
+		bash -n $$f || exit 1; done
+	@if command -v shellcheck >/dev/null; then \
+		shellcheck -x bin/opencode-sandbox lib/*.sh egress/entrypoint.sh shim/xdg-open; \
+	else echo "shellcheck not installed — syntax only"; fi
+	@echo "✓ lint"