Proposal: Extend llms.txt to installed packages to support local filesystem resolution

llms.txt already targets the developer use case; the spec explicitly mentions "coding library documentation" and "development environments" as key scenarios. The convention works well when an agent is browsing the web for information or docs.

However, when a coding agent is working locally with an installed dependency, the package is already on disk. The agent already resolved the import to a directory. A web fetch for information is less efficient than co-location with the code. It is slower, can introduce version mismatch, and unhelpful for private or internal-only packages.

**Proposed Extension**
Packages should ship a llms.txt at their root, and agents should read it when they encounter that package.

Resolution Rule:
import foo -> resolves foo's install path -> read /llms.txt if present

This mirrors the existing web convention: agents just resolve from /llms.txt rather than /llms.txt. The solution works for any ecosystem where an import resolves locally.

Package authors ship llms.txt alongside their source. Agent runtimes update to run a single stat prior to source exploration for an unfamiliar import. Private and internal packages have a non-domain dependent support path.

Start by reviewing the existing llms.txt specification and the documented package-author and agent use cases. Define how local package resolution, package versions, and agent behavior should be specified; done means the proposal has an agreed resolution rule and clear documentation for package authors and agent runtimes.

Written by the indexing model from the issue text.