Candidates: inline rename (fix a name typo without reject + re-add)

A staged candidate could only be renamed by rejecting and re-adding it, which
churns the queue and discards the preview just to fix a typo. Add an inline
Rename on each candidate: a "Rename" pill swaps the name for an input
(Enter saves · Esc cancels), POST /api/admin/candidates/{id}/rename →
sources.rename_candidate(). Empty clears the name (promote then derives one
from the feed host). Preview is preserved; the fixed name carries into promotion.

Tests: test_candidate_rename (rename in place keeps preview, promotes with the
new name, gated + 404). 225 pytest + 11 vitest green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

goodnews/sources.py

@@ -153,6 +153,19 @@ def list_candidates(conn: sqlite3.Connection, status: str | None = None) -> list
     return conn.execute("SELECT * FROM source_candidates ORDER BY updated_at DESC").fetchall()
 
 
+def rename_candidate(conn: sqlite3.Connection, candidate_id: int, name: str | None) -> sqlite3.Row:
+    """Fix a staged candidate's display name without re-fetching it. An empty
+    name clears it (promote then derives one from the feed host)."""
+    cur = conn.execute(
+        "UPDATE source_candidates SET name = ?, updated_at = CURRENT_TIMESTAMP WHERE id = ?",
+        (name or None, candidate_id),
+    )
+    conn.commit()
+    if cur.rowcount == 0:
+        raise ValueError(f"no candidate with id {candidate_id}")
+    return conn.execute("SELECT * FROM source_candidates WHERE id = ?", (candidate_id,)).fetchone()
+
+
 def reject_candidate(conn: sqlite3.Connection, candidate_id: int) -> bool:
     cur = conn.execute(
         "UPDATE source_candidates SET status = 'rejected', updated_at = CURRENT_TIMESTAMP WHERE id = ?",