fix(mod-loader): support subdir streaming entries (ped head_ ydd/ytd) in mods/

[chocomintw]

Goal of this PR

Make OpenIV-style mod packages in mods/ able to replace ped component files that live in a subdirectory of a streaming rpf — most notably head_*.ydd / head_diff_*.ytd in x64v.rpf/models/cdimages/streamedpeds_mp.rpf/mp_m_freemode_01/ (and streamedpeds_players.rpf/player_zero/). Today such entries are silently dropped.

How is this PR achieving the goal

The game registers these assets under a directory-prefixed slot name (mp_m_freemode_01/head_000_r), which is why resource stream/ uses the dir^file convention. The mod loader lost that directory at three points:

1. ModVFSDevice only mapped entries whose last archive is update.rpf, a top-level x64N.rpf, or common.rpf; nested archives fell through.
2. MountModStream required slashCount == 0, so mp_m_freemode_01/head_000_r.ydd was never registered as a streaming file.
3. The ^ → / subdir mapping in LoadStreamingFile.cpp is gated on the server policy [subdir_file_mapping], which doesn't exist at OnInitialMount (no server yet).

Changes:

• gta-streaming-five: GetBaseName() takes an isMod flag; mod_ / faux_pack tags get subdir mapping without the server policy. Resource behaviour is unchanged. Small IsModTag() helper replaces the inline check.
• citizen-mod-loader-five: nested-archive entries with a subdirectory target are exposed by ModVFSDevice as stream/<dir>^<file> and registered from MountModStream as modVfs_<guid>:/stream/<dir>^<file>, so the streaming slot keeps its directory. Flat entries and textures/ overrides register exactly as before.

Not covered: a whole streamedpeds_*.rpf dropped in as an .rpf target (MountFauxStreamingRpf is non-recursive, and a packfile can't serve a ^ name).

This PR applies to the following area(s)

FiveM

Successfully tested on

Compiles (Release x64, no new warnings). Not yet tested in-game — will update once verified.

Game builds: ..

Platforms: Windows

Checklist

• Code compiles and has been tested successfully.
• Code explains itself well and/or is documented.
• My commit message explains what the changes do and what they are for.
• No extra compilation warnings are added by these changes.

Fixes issues

None.