feat(installer): support --key=value CLI flags

[MioYuuIH]

Summary

• Add CLI flag parsing (--gpu, --docker, --mirror, --mirror-pip, --mirror-npm) as alternatives to environment variables
• Flags can appear in any position and override corresponding env vars
• Update help text to document new flag syntax

Before: GPU_TYPE=strix ./auplc-installer install
After: ./auplc-installer install --gpu=strix

All flags:

Flag	Env Variable	Example
--gpu=TYPE	GPU_TYPE	--gpu=strix-halo
--docker=0|1	K3S_USE_DOCKER	--docker=0
--mirror=PREFIX	MIRROR_PREFIX	--mirror=m.daocloud.io
--mirror-pip=URL	MIRROR_PIP	--mirror-pip=https://pypi.tuna.edu.cn/simple
--mirror-npm=URL	MIRROR_NPM	--mirror-npm=https://registry.npmmirror.com

Test plan

• Verified CLI flag parsing for all argument combinations and positions
• Verified generated YAML is valid for all GPU types (phx, strix, strix-halo)
• Verified deep merge with values.yaml produces correct accelerator env and image tags
• Verified strix correctly gets HSA_OVERRIDE_GFX_VERSION=11.0.0 + gfx110x images
• Verified strix-halo correctly uses native gfx1151 images without HSA override