feat: Filter backend gallery by system capabilities (#7950)

* Initial plan

* Add backend gallery filtering based on system capabilities

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Refactor L4T backend check to come before NVIDIA check

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Refactor: move capabilities business logic to capabilities.go and use constants

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* feat: display system capability in webui and refactor tests

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* chore: rename System/Capability

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* refactor: use getSystemCapabilities in IsBackendCompatible for consistency

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* refactor: keep unused constants private in capabilities.go

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* fix: skip AMD/ROCm and Intel/SYCL tests on darwin

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

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Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>