Initial Arka plugin registry: Official plugins mirror + Arka-signed index

11 plugins from github.com/librefang/librefang-registry plugins/.
index.json / index.json.sig are signed with Arka's Ed25519 key
(not upstream stats.librefang.ai). Private key is not in this repo.

plugins/conversation-logger/README.md

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+# conversation-logger
+
+Logs all conversations to JSONL files for auditing, analytics, and debugging. Each agent gets its own log file at `~/.librefang/logs/conversations/{agent_id}.jsonl`.
+
+## Log Format
+
+Each line is a JSON object:
+
+```json
+{
+  "timestamp": "2026-03-21T12:34:56Z",
+  "agent_id": "agent-abc123",
+  "turn_number": 5,
+  "message_count": 10,
+  "last_user_message": "truncated to 200 chars...",
+  "last_assistant_message": "truncated to 200 chars..."
+}
+```
+
+## Hooks
+
+| Hook | Script | Description |
+|------|--------|-------------|
+| after_turn | `hooks/after_turn.py` | Appends a log entry after each conversation turn |
+
+## How It Works
+
+After each conversation turn the hook extracts summary information from the messages array and appends a single JSON line to the agent's log file. User and assistant messages are truncated to 200 characters to keep log files manageable.
+
+Errors from the filesystem (permissions, disk full, etc.) are caught silently so the agent conversation is never interrupted by a logging failure.
+
+## Usage
+
+Installed automatically when enabled in agent configuration. Log files are created on first write -- no manual setup required.