Release v1.26.0

Slack can now deliver generated files and keep channel, thread, and allowlisted direct-message conversations in separate sessions. Top-level mentions reply directly in the channel; threaded mentions stay in their parent thread.

• Deliver provider-generated files, including file-only responses, with cancellation and restart recovery. Interrupted deliveries are retained for reconciliation rather than automatically retried.
• Expose secure file-download and video-transcode tools for Slack, alongside attachment registration.
• Add host-derived chat classification for Slack conversations, rejecting inconsistent thread identities during replay.
• Configure Codex hosted web search with CODEX_WEB_SEARCH_MODE (disabled, cached, indexed, or live; default cached). This is separate from sandboxed-command network access.
• Convert empty legacy read-only Codex credential-directory placeholders into directories while preserving ambiguous files and rejecting symlinks.
• Update MCP SDK, dotenv, and Node types, and move the Docker build cache to GHCR.

Slack setup: add the files:write bot scope for response uploads. Replies inside DM threads are unsupported; send a top-level DM instead. For direct messages, add im:read and im:history and subscribe to message.im. Reinstall the Slack app after changing scopes. Restart the application after changing the Codex search setting.

Container image: ghcr.io/rubiss-projects/ai-assistant:v1.26.0 (linux/amd64 and linux/arm64).

PR: #110