Add Aider provider adapter

## Goal Add Aider as a Lineage provider target. ## Why Aider is a widely used terminal-based AI coding assistant and is relevant for users who prefer local CLI workflows. ## Scope - Define the Aider adapter boundary. - Detect or configure the `aider` command where available. - Decide which package assets can map to Aider conventions, config, or launch arguments. - Avoid packaging provider credentials or local model keys. - Add dry-run/inspect output showing what Aider support will do. ## Acceptance Criteria - Aider support is behind an explicit provider adapter. - Tests cover launch planning/materialization behavior Lineage owns. - No local credentials or model keys are packaged. - Docs explain required local Aider setup and current limitations.