feat: update file querying methods to support flat directory structur…

[TzuHuanTai]

…e for timelapse videos

[Copilot]

Pull request overview

This PR updates the RTC datachannel “query file” flow and filesystem utilities to support querying video files from either the existing nested recording directory layout (root/YYYYMMDD/HH/) or a flat directory layout intended for timelapse videos.

Changes:

• Extend Conductor::SendFileResponse and QueryFileResponse sending to include a VideoMode to distinguish recording vs timelapse queries.
• Replace “second newest file” lookup with Utils::FindLatestCompleteFile(...) and update older/time-based queries to accept a base_dir.
• Add flat-layout handling paths in Utils::FindLatestCompleteFile, FindFilesFromDatetime, and FindOlderFiles.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

File	Description
src/rtc/conductor.h	Updates SendFileResponse signature to include video mode.
src/rtc/conductor.cpp	Routes queries to mode-specific base directories and includes mode in responses.
src/common/utils.h	Renames/extends file-query utility APIs to accept a base directory and adds FindLatestCompleteFile.
src/common/utils.cpp	Implements flat vs nested directory handling for latest/older/time-based file queries.

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