make `apr import` have `--output` as optional

[alfredodeza]

The idea here is that importing a model should automatically replace the suffix with .apr and keep the original model name. This makes the terminal interaction a bit easier since the user doesn't need to type the whole model name again with the .apr suffix. It is also easier on new users that may not understand that apr import does a conversion into the .apr format.

What happens currently:

apr import hf://Qwen/Qwen2.5-1.5B-Instruct-GGUF/resolve/main/qwen2.5-1.5b-instruct-q4_k_m.gguf
error: the following required arguments were not provided:
  --output <OUTPUT>

Usage: apr import --output <OUTPUT> <SOURCE>

For more information, try '--help'.

By making --output optional, it allows the user to control the final naming convention of the imported model, but allows an easier interaction with users that prefer to keep things as-is. This is how it should work ideally:

apr import hf://Qwen/Qwen2.5-1.5B-Instruct-GGUF/resolve/main/qwen2.5-1.5b-instruct-q4_k_m.gguf
=== APR Import Pipeline ===

Source: /home/alfredo/Downloads/qwen2.5-1.5b-instruct-q4_k_m.gguf (Local)
Output: qwen2.5-1.5b-instruct-q4_k_m.apr

Architecture: Auto
Validation: Strict

Importing...
[DEBUG-CLI] About to call apr_import with source= hf://Qwen/Qwen2.5-1.5B-Instruct-GGUF/resolve/main/qwen2.5-1.5b-instruct-q4_k_m.gguf
[DEBUG] apr_import called: source= hf://Qwen/Qwen2.5-1.5B-Instruct-GGUF/resolve/main/qwen2.5-1.5b-instruct-q4_k_m.gguf
[DEBUG] extension=gguf
[PMAT-114 DEBUG] apr_import_gguf_raw called - gguf_path= hf://Qwen/Qwen2.5-1.5B-Instruct-GGUF/resolve/main/qwen2.5-1.5b-instruct-q4_k_m.gguf
=== Validation Report ===
Score: 85/100 (Grade: B+)

⚠ Import completed with warnings

[noahgift]

✅ FIXED (PMAT-185) - Made --output optional, uses default cache when omitted. Refs: PMAT-185