⚙️ FEATURE-#58: Resolve bundled provider templates by bare name

[FernandoCelmer]

Description

• pycodeloop/providers/__init__.py — Adds BUNDLED_TEMPLATES, the set of template stems discovered from providers/templates/*.json at import time. get_provider() resolves a bare name in that set (e.g. "anthropic", "ollama") to the packaged JSON path before falling through to the PROVIDERS registry or module:Class syntax. Extracted the JSON-loading branch into _from_json_path() so both the path and bare-name cases share it.
• pycodeloop/cli/flow.py — resolve_provider() now treats a bundled template name the same as a .json path when building kwargs, so it doesn't force-override the template's own model with Settings.MODEL when --model isn't passed.

Motivation and Context

--provider required a full/relative path to a JSON template, so running the CLI from outside the repo always needed the full path to pycodeloop/providers/templates/*.json. Now the bundled templates resolve by short name from anywhere the package is installed:

pycodeloop --provider anthropic
pycodeloop --provider ollama
pycodeloop run "..." --provider openai --model gpt-5

Closes #58.

Types of changes

• New feature (change which adds functionality)
• Bug fix
• Documentation

Checklist

• I have performed a self-review of my own code
• I have added tests that prove my feature works
• I have updated the CHANGELOG
• I have updated the documentation accordingly