feat: Project-based context management (version-aware)

[thiagozf]

Support organizing documentation context by project, allowing each project to specify which version of a library it uses.

• A project references specific libraries (e.g. @libcontext/core@1.2.0, react@18.2.0)
• LibContext indexes and serves context scoped to the project the user is currently working on
• We should avoid reprocessing shared library versions between projects
• CLI should allow --project my-app and load correct context

This enables more accurate context injection for coding assistants that need to align with the actual versions used in a project.

Open questions:

• How can the IDE to select the project user is currently working? Maybe a per-project MCP server setup?