Establish versioned GitHub Releases for the LPP contract

[Teakowa]

Goal

Establish the same lightweight Release Please lifecycle already used by Wright, adapted to LPP's repository-only GitHub Releases.

Scope

• Track the LPP repository release version in version.txt.
• Align repository release SemVer with the protocol line: v1.1.0 corresponds to LPP 1.1, additive LPP 1.2 starts at v1.2.0, and a breaking LPP 2.0 starts at v2.0.0.
• Allow patch repository releases such as v1.1.1 for spec/conformance/release fixes that do not define a new wire version.
• Use Release Please to maintain release PRs, tags, changelog, and GitHub Releases from main.
• Reuse Wright's GH_TOKEN-based release workflow pattern so generated release PRs participate in normal repository CI.
• Keep the existing Rust/conformance CI as the release PR gate.

Non-goals

• Publishing any crate to crates.io.
• Building or publishing binary artifacts.
• Changing LPP wire semantics or conformance behavior as part of the release plumbing.
• Coupling the Cargo package versions of conformance tooling to the protocol release version.

Acceptance Criteria

• Release Please can maintain a SemVer release PR and create a Git tag/GitHub Release after merge.
• Repository release major/minor matches the corresponding LPP wire major/minor.
• Patch repository releases can fix the published contract/tooling without implying a new wire version.
• Existing Rust and conformance CI remains unchanged and gates release PRs normally.
• No crates.io or binary distribution workflow is introduced.

Ownership

Owning repository: wrightkit/language-provider-protocol.

[Teakowa]

Implementation is proceeding on release/lpp-github-releases. Scope is limited to GitHub Release/version plumbing and existing conformance gates; no crates.io publication or Wright distribution pipeline.