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>

llama_stack/cli/llama.py

@@ -6,11 +6,8 @@
 
 import argparse
 
-from .download import Download
-from .model import ModelParser
 from .stack import StackParser
 from .stack.utils import print_subcommand_description
-from .verify_download import VerifyDownload
 
 
 class LlamaCLIParser:
@@ -30,10 +27,7 @@ class LlamaCLIParser:
         subparsers = self.parser.add_subparsers(title="subcommands")
 
         # Add sub-commands
-        ModelParser.create(subparsers)
         StackParser.create(subparsers)
-        Download.create(subparsers)
-        VerifyDownload.create(subparsers)
 
         print_subcommand_description(self.parser, subparsers)