feat(providers): added ollama support and openai

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Pull request overview

This PR adds support for multiple LLM providers (OpenAI and Ollama) alongside the existing Anthropic integration, introducing a provider abstraction layer and updating the codebase to use standardized model naming conventions.

Changes:

• Introduced provider abstraction with base classes and implementations for Anthropic, OpenAI, and Ollama
• Refactored model naming from descriptive names (e.g., "Claude Haiku 3") to standardized identifiers (e.g., "claude-haiku")
• Updated cost tracking to handle free local models and new provider structure

Reviewed changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/harvestor/providers/base.py	New base provider abstraction defining the interface for all LLM providers
src/harvestor/providers/anthropic.py	Anthropic provider implementation with Claude models
src/harvestor/providers/openai.py	OpenAI provider implementation with GPT models
src/harvestor/providers/ollama.py	Ollama provider implementation for local models
src/harvestor/providers/init.py	Provider registry and factory function
src/harvestor/parsers/llm_parser.py	Refactored to use provider abstraction instead of direct Anthropic client
src/harvestor/core/harvestor.py	Updated to support multi-provider initialization and removed direct Anthropic dependencies
src/harvestor/core/cost_tracker.py	Updated to handle free models and new pricing structure
src/harvestor/config.py	Refactored to re-export provider models for backwards compatibility
src/harvestor/schemas/base.py	Added new provider-based extraction strategies
tests/*.py	Updated test patches and model references to use new naming conventions
example.py	Updated to demonstrate multi-provider usage
src/harvestor/cli/main.py	Added model listing functionality and updated default model

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