feat: migrate A2A crates to a2aproj-a2a-rs namespace

[muscariello]

Summary

• rename published A2A crate package names from agntcy-a2a* to a2aproj-a2a-rs*
• update forward-facing repository references from agntcy/a2a-rs to a2aproject/a2a-rs
• keep historical changelog tag names and release references unchanged where they refer to past published artifacts

Validation

• cargo test --workspace --quiet
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings

[gemini-code-assist]

Code Review

This pull request performs a comprehensive renaming of the project and its crates, transitioning from the agntcy namespace to a2aproject and lf-a2a. The changes span repository URLs, package definitions, and documentation across the entire workspace. A review comment correctly identifies a version inconsistency in the a2a-server README example, which should be updated to reflect the current crate version for accuracy.

[gemini-code-assist]

The version specified in the dependency example for lf-a2a-server is 0.1, but the actual version of the crate in a2a-server/Cargo.toml is 0.2.6. This should be updated to 0.2 to match the current major/minor version and maintain consistency with the other crates in the workspace.

Suggested change

	a2a-server = { package = "lf-a2a-server", version = "0.1" }
	a2a-server = { package = "lf-a2a-server", version = "0.2" }