feat(cli): add 'lore related' semantic similarity command (bd-8con)

Adds 'lore related' / 'lore similar' command for discovering semantically
related issues and MRs using vector embeddings.

Two modes:
- Entity mode: find entities similar to a specific issue/MR
- Query mode: embed free text and find matching entities

Includes distance-to-similarity conversion, label intersection,
human and robot output formatters, and 11 unit tests.

src/gitlab/client.rs

@@ -112,6 +112,20 @@ impl GitLabClient {
         self.request("/api/v4/version").await
     }
 
+    pub async fn get_issue_by_iid(&self, gitlab_project_id: i64, iid: i64) -> Result<GitLabIssue> {
+        let path = format!("/api/v4/projects/{gitlab_project_id}/issues/{iid}");
+        self.request(&path).await
+    }
+
+    pub async fn get_mr_by_iid(
+        &self,
+        gitlab_project_id: i64,
+        iid: i64,
+    ) -> Result<GitLabMergeRequest> {
+        let path = format!("/api/v4/projects/{gitlab_project_id}/merge_requests/{iid}");
+        self.request(&path).await
+    }
+
     const MAX_RETRIES: u32 = 3;
 
     async fn request<T: serde::de::DeserializeOwned>(&self, path: &str) -> Result<T> {
@@ -848,4 +862,143 @@ mod tests {
         let result = parse_link_header_next(&headers);
         assert!(result.is_none());
     }
+
+    // ─────────────────────────────────────────────────────────────────
+    //  get_issue_by_iid / get_mr_by_iid
+    // ─────────────────────────────────────────────────────────────────
+
+    use wiremock::matchers::{header, method, path};
+    use wiremock::{Mock, MockServer, ResponseTemplate};
+
+    fn mock_issue_json(iid: i64) -> serde_json::Value {
+        serde_json::json!({
+            "id": 1000 + iid,
+            "iid": iid,
+            "project_id": 42,
+            "title": format!("Issue #{iid}"),
+            "description": null,
+            "state": "opened",
+            "created_at": "2024-01-15T10:00:00.000Z",
+            "updated_at": "2024-01-16T12:00:00.000Z",
+            "closed_at": null,
+            "author": { "id": 1, "username": "alice", "name": "Alice", "avatar_url": null },
+            "assignees": [],
+            "labels": ["bug"],
+            "milestone": null,
+            "due_date": null,
+            "web_url": format!("https://gitlab.example.com/g/p/-/issues/{iid}")
+        })
+    }
+
+    fn mock_mr_json(iid: i64) -> serde_json::Value {
+        serde_json::json!({
+            "id": 2000 + iid,
+            "iid": iid,
+            "project_id": 42,
+            "title": format!("MR !{iid}"),
+            "description": null,
+            "state": "opened",
+            "draft": false,
+            "work_in_progress": false,
+            "source_branch": "feat",
+            "target_branch": "main",
+            "sha": "abc123",
+            "references": { "short": format!("!{iid}"), "full": format!("g/p!{iid}") },
+            "detailed_merge_status": "mergeable",
+            "created_at": "2024-02-01T08:00:00.000Z",
+            "updated_at": "2024-02-02T09:00:00.000Z",
+            "merged_at": null,
+            "closed_at": null,
+            "author": { "id": 2, "username": "bob", "name": "Bob", "avatar_url": null },
+            "merge_user": null,
+            "merged_by": null,
+            "labels": [],
+            "assignees": [],
+            "reviewers": [],
+            "web_url": format!("https://gitlab.example.com/g/p/-/merge_requests/{iid}"),
+            "merge_commit_sha": null,
+            "squash_commit_sha": null
+        })
+    }
+
+    fn test_client(base_url: &str) -> GitLabClient {
+        GitLabClient::new(base_url, "test-token", Some(1000.0))
+    }
+
+    #[tokio::test]
+    async fn get_issue_by_iid_success() {
+        let server = MockServer::start().await;
+
+        Mock::given(method("GET"))
+            .and(path("/api/v4/projects/42/issues/7"))
+            .and(header("PRIVATE-TOKEN", "test-token"))
+            .respond_with(ResponseTemplate::new(200).set_body_json(mock_issue_json(7)))
+            .mount(&server)
+            .await;
+
+        let client = test_client(&server.uri());
+        let issue = client.get_issue_by_iid(42, 7).await.unwrap();
+
+        assert_eq!(issue.iid, 7);
+        assert_eq!(issue.title, "Issue #7");
+        assert_eq!(issue.state, "opened");
+    }
+
+    #[tokio::test]
+    async fn get_issue_by_iid_not_found() {
+        let server = MockServer::start().await;
+
+        Mock::given(method("GET"))
+            .and(path("/api/v4/projects/42/issues/999"))
+            .respond_with(ResponseTemplate::new(404))
+            .mount(&server)
+            .await;
+
+        let client = test_client(&server.uri());
+        let err = client.get_issue_by_iid(42, 999).await.unwrap_err();
+
+        assert!(
+            matches!(err, LoreError::GitLabNotFound { .. }),
+            "Expected GitLabNotFound, got: {err:?}"
+        );
+    }
+
+    #[tokio::test]
+    async fn get_mr_by_iid_success() {
+        let server = MockServer::start().await;
+
+        Mock::given(method("GET"))
+            .and(path("/api/v4/projects/42/merge_requests/99"))
+            .and(header("PRIVATE-TOKEN", "test-token"))
+            .respond_with(ResponseTemplate::new(200).set_body_json(mock_mr_json(99)))
+            .mount(&server)
+            .await;
+
+        let client = test_client(&server.uri());
+        let mr = client.get_mr_by_iid(42, 99).await.unwrap();
+
+        assert_eq!(mr.iid, 99);
+        assert_eq!(mr.title, "MR !99");
+        assert_eq!(mr.source_branch, "feat");
+        assert_eq!(mr.target_branch, "main");
+    }
+
+    #[tokio::test]
+    async fn get_mr_by_iid_not_found() {
+        let server = MockServer::start().await;
+
+        Mock::given(method("GET"))
+            .and(path("/api/v4/projects/42/merge_requests/999"))
+            .respond_with(ResponseTemplate::new(404))
+            .mount(&server)
+            .await;
+
+        let client = test_client(&server.uri());
+        let err = client.get_mr_by_iid(42, 999).await.unwrap_err();
+
+        assert!(
+            matches!(err, LoreError::GitLabNotFound { .. }),
+            "Expected GitLabNotFound, got: {err:?}"
+        );
+    }
 }