Add support for attestation commit

[alexr00]

No description provided.

[Copilot]

Pull request overview

This PR adds an “attestation commit” capability to the GitHub Pull Requests extension, allowing users to optionally create and push an empty signed commit to the PR branch (and to request that flow during review submission) to attest to a PR even when individual commits are unsigned.

Changes:

• Adds a new githubPullRequests.enableAttestationCommits setting plus a new pr.addAttestationCommit command, and introduces src/github/attestationCommit.ts to implement the feature.
• Extends review submission messaging so webviews can request an attestation commit before submitting a review, and updates timeline ordering logic to avoid misclassifying pre-review attestation commits as “new since review”.
• Updates the PR comment UI to include an “Add attestation” checkbox when applicable.

Show a summary per file

File	Description
webviews/components/comment.tsx	Adds “Add attestation” checkbox and forwards an addAttestation flag through review submit actions.
webviews/common/context.tsx	Updates webview->extension review submission payload shape to include { body, addAttestation }.
webviews/common/common.css	Adds styling for the new attestation checkbox and right-aligned action grouping.
webviews/activityBarView/index.css	Adds overlay positioning for the checkbox in the activity bar PR view.
src/github/views.ts	Extends PR view models with attestationCommitsEnabled and introduces SubmitReviewArgs.
src/github/utils.ts	Refines “new commits since review” ordering using timestamps (attestation-aware behavior).
src/github/pullRequestOverview.ts	Implements “submit review with optional attestation commit” handling and exposes feature enablement to the webview.
src/github/issueOverview.ts	Adjusts issue comment submission to accept SubmitReviewArgs and uses args.body.
src/github/attestationCommit.ts	New implementation for creating/pushing an empty signed attestation commit and reading the related setting.
src/github/activityBarViewProvider.ts	Adds the same “review with optional attestation commit” handling for the activity bar PR view.
src/common/settingKeys.ts	Adds ENABLE_ATTESTATION_COMMITS setting key constant.
src/commands.ts	Registers pr.addAttestationCommit command (command palette / programmatic entry point).
package.nls.json	Adds localized strings for the new setting description and command title.
package.json	Contributes the new setting and command to the extension manifest.

Copilot's findings

• Files reviewed: 14/14 changed files
• Comments generated: 7

[Copilot]

Copilot's findings

Comments suppressed due to low confidence (1)

src/github/utils.ts:1707

• The loop in insertNewCommitsSinceReview never evaluates i === 0, so if latestReviewCommitOid is the first timeline event (a valid case), the NewCommitsSinceReview marker is never inserted. This also makes the new unit tests fail when the latest-review commit is at index 0.

	if (latestReviewCommitOid && head && head.sha !== latestReviewCommitOid) {
		let lastViewerReviewIndex: number = timelineEvents.length - 1;
		let lastViewerReviewTime: number | undefined;
		let comittedDuringReview: boolean = false;
		let interReviewCommits: Common.TimelineEvent[] = [];

		for (let i = timelineEvents.length - 1; i > 0; i--) {

• Files reviewed: 15/15 changed files
• Comments generated: 4