v0.6.0 — Session persistence & agent completion fixes

[v0.6.0] — 2026-06-24

Added

• Session persistence across restarts — SessionMap now persists
  chatCurrent and topicBind mappings to ~/.config/omotg/sessions_<bot>.json.
  Chat and topic session bindings survive server restarts, so conversations
  continue with the same OpenCode session (and its full history) instead of
  creating a new blank session.
• Dynamic child timeout — child agent timeout timer resets on every SSE
  event, so long-running sub-agents are only interrupted when truly idle (60s),
  not when they are actively producing output.
• Completion reason logging — every exit path from processMessage logs
  a structured reason field (completed, session_timeout, child_timeout,
  send_message_error, sse_unavailable) for observability.

Fixed

• Agent completion reports missing — 5 root causes fixed where agent output
  never reached Telegram: SSE stream death + slow POST response now retries and
  notifies user; successful responses append completion marker; child and session
  timeouts send explicit Telegram messages instead of silently returning;
  handleMsgResult now correctly sets *mainTextSent.
• MCP endpoint URL — opencode.json URL corrected from /mcp (404) to
  /mcp/sse (200), enabling agents to call send_telegram_message and
  send_telegram_notification tools.
• Rate limiting — sendTelegram enforces 500ms minimum gap between sends
  to avoid Telegram "Too Many Requests" errors from burst tool notifications.