chore!: remove model mgmt from CLI for Hugging Face CLI (#3700)

This change removes the `llama model` and `llama download` subcommands
from the CLI, replacing them with recommendations to use the Hugging
Face CLI instead.

Rationale for this change:
- The model management functionality was largely duplicating what
Hugging Face CLI already provides, leading to unnecessary maintenance
overhead (except the download source from Meta?)
- Maintaining our own implementation required fixing bugs and keeping up
with changes in model repositories and download mechanisms
- The Hugging Face CLI is more mature, widely adopted, and better
maintained
- This allows us to focus on the core Llama Stack functionality rather
than reimplementing model management tools

Changes made:
- Removed all model-related CLI commands and their implementations
- Updated documentation to recommend using `huggingface-cli` for model
downloads
- Removed Meta-specific download logic and statements
- Simplified the CLI to focus solely on stack management operations

Users should now use:
- `huggingface-cli download` for downloading models
- `huggingface-cli scan-cache` for listing downloaded models

This is a breaking change as it removes previously available CLI
commands.

Signed-off-by: Sébastien Han <seb@redhat.com>

uv.lock

@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 2
 requires-python = ">=3.12"
 resolution-markers = [
     "(python_full_version >= '3.13' and platform_machine != 'aarch64' and sys_platform == 'linux') or (python_full_version >= '3.13' and sys_platform != 'darwin' and sys_platform != 'linux')",
@@ -1774,7 +1774,6 @@ dependencies = [
     { name = "fire" },
     { name = "h11" },
     { name = "httpx" },
-    { name = "huggingface-hub" },
     { name = "jinja2" },
     { name = "jsonschema" },
     { name = "llama-stack-client" },
@@ -1896,7 +1895,6 @@ requires-dist = [
     { name = "fire" },
     { name = "h11", specifier = ">=0.16.0" },
     { name = "httpx" },
-    { name = "huggingface-hub", specifier = ">=0.34.0,<1.0" },
     { name = "jinja2", specifier = ">=3.1.6" },
     { name = "jsonschema" },
     { name = "llama-stack-client", specifier = ">=0.2.23" },