fix: validate gitea_edit_pr no-fields before authentication (#43)

gitea_edit_pr called _auth() (and resolved the remote) before checking whether
any editable field was provided, so a pure validation error (no fields) surfaced
as a RuntimeError "no credentials" in environments without Gitea auth — making
test_edit_pr_no_fields_raises depend on credentials/network/env.

Move the payload build + no-fields ValueError ahead of _resolve/_auth/URL setup.
Behavior is unchanged when fields are provided (same _resolve → _auth → audited
PATCH path). No change to auth, retry/backoff, audit, config profiles, or
worktree helpers.

Tests: add test_edit_pr_no_fields_validates_before_auth asserting the no-fields
path raises ValueError and calls neither get_auth_header nor api_request (even
with auth mocked to None). Existing edit-PR tests unchanged.

Full suite passes with no Gitea credentials (287 passed, 0 failures) — the
no-fields test no longer depends on the environment.

Closes #43.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mcp_server.py

@@ -720,9 +720,9 @@ def gitea_edit_pr(
     Returns:
         dict with success status and details of the edited PR.
     """
-    h, o, r = _resolve(remote, host, org, repo)
-    auth = _auth(h)
-    url = f"{repo_api_url(h, o, r)}/pulls/{pr_number}"
+    # Validate inputs BEFORE any auth/profile resolution or API setup: a
+    # no-fields call is a pure validation error and must not depend on
+    # credentials, network, or environment configuration.
     payload = {}
     if title is not None:
         payload["title"] = title
@@ -736,6 +736,10 @@ def gitea_edit_pr(
     if not payload:
         raise ValueError("At least one field to edit (title, body, state, base) must be provided.")
 
+    h, o, r = _resolve(remote, host, org, repo)
+    auth = _auth(h)
+    url = f"{repo_api_url(h, o, r)}/pulls/{pr_number}"
+
     with _audited("edit_pr", host=h, remote=remote, org=o, repo=r,
                   pr_number=pr_number, request_metadata={"fields": sorted(payload)}):
         data = api_request("PATCH", url, auth, payload)