feat: self-request as reviewer before posting

Closes #35

Before posting a review, the bot:
1. Discovers its own Gitea login via GET /user
2. Calls POST /requested_reviewers to add itself

This ensures the bot appears in the required-reviewers list without
manual configuration on the repo. The call is idempotent (no-op if
already requested).

Both failures are non-fatal (warn + continue) — the review still posts
even if the self-request fails.

gitea/client.go

@@ -460,3 +460,56 @@ func (c *Client) EditComment(ctx context.Context, owner, repo string, commentID
 	}
 	return nil
 }
+
+// GetAuthenticatedUser returns the login of the user authenticated by the token.
+func (c *Client) GetAuthenticatedUser(ctx context.Context) (string, error) {
+	reqURL := fmt.Sprintf("%s/api/v1/user", c.baseURL)
+	body, err := c.doGet(ctx, reqURL)
+	if err != nil {
+		return "", fmt.Errorf("get authenticated user: %w", err)
+	}
+	var result struct {
+		Login string `json:"login"`
+	}
+	if err := json.Unmarshal(body, &result); err != nil {
+		return "", fmt.Errorf("parse user response: %w", err)
+	}
+	return result.Login, nil
+}
+
+// RequestReviewer adds the given user as a requested reviewer on a pull request.
+// This is idempotent — requesting an already-requested reviewer is a no-op.
+func (c *Client) RequestReviewer(ctx context.Context, owner, repo string, number int, reviewer string) error {
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/requested_reviewers",
+		c.baseURL,
+		url.PathEscape(owner),
+		url.PathEscape(repo),
+		number)
+
+	payload := struct {
+		Reviewers []string `json:"reviewers"`
+	}{Reviewers: []string{reviewer}}
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal reviewer request: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, reqURL, bytes.NewReader(data))
+	if err != nil {
+		return fmt.Errorf("create reviewer request: %w", err)
+	}
+	req.Header.Set("Authorization", "token "+c.token)
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return fmt.Errorf("request reviewer: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusCreated {
+		body, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("request reviewer failed (status %d): %s", resp.StatusCode, body)
+	}
+	return nil
+}