Add Ollama provider support and refine-with-note option

[infpdev]

Summary

Add native support for running scom against a local Ollama server, improve refine guidance handling

I mainly implemented this so I could use Ollama as the primary provider locally while still keeping cloud models available as fallbacks when needed..

Related issue

Closes #9

What changed

• Added an ollama provider without API-key requirements and routed Ollama requests through /api/tags and /api/generate.
• Added local model discovery with automatic fallback to an installed Ollama model when the configured model is unavailable.
• Added "Refine with Note" so users can steer the next generation directly without reusing the previous draft as prompt context.
• Stopped truncating staged diffs before generation.
• Updated setup/model flows so Ollama skips API-key prompts and supports a configurable local base URL.
• Updated the README with the minimum required Ollama setup and usage notes.

Testing

• Verified scom setup with Ollama selected as provider.
• Verified local model discovery through /api/tags.
• Verified generation through /api/generate.
• Verified fallback to an installed local model when the configured model is unavailable.
• Verified "Refine with Note" influences regeneration while preserving selected output style.
• Verified staged diffs are passed without truncation.

Manual checks

• Confirm Ollama model discovery uses GET /api/tags.
• Confirm generation uses POST /api/generate with model fallback.
• Confirm "Refine with Note" respects the selected output style (short, detailed, adaptive).
• Confirm staged diffs are passed in full.
• Confirm Ollama falls back to an installed model when the configured model is unavailable.

Preview

Example of using a local Ollama model together with the interactive "Refine with Note" workflow:

Checklist

• The PR targets dev. (The contributing guide mentions targeting dev, but the repository currently only exposes main, so this PR targets main instead)
• The related issue is linked in the PR description.
• Tests added or updated where appropriate. (No tests currently exist in the main branch.)
• Linter/formatting passes locally.
• Documentation updated if public behavior changed.