feat: offer guided repair when loading a broken config file

If a config file on disk fails strict JSON parsing, BCC now runs it
through the same repair pipeline as pasted snippets and shows a dialog
listing the parse error, each fix it would apply, and a preview of the
resulting file. The user chooses: Repair & load (marks the profile
dirty; the file is only rewritten on Save, after the broken original
is backed up) or Cancel. Unsalvageable files keep the old error path.

repair_config_file() in bcc_core never writes to disk itself.

bcc_core.py

@@ -132,6 +132,33 @@ def load_config(path: str | os.PathLike) -> dict:
     return obj
 
 
+def repair_config_file(path: str | os.PathLike) -> tuple[dict, list[str], str]:
+    """
+    Attempt to repair a config file that failed strict parsing, WITHOUT writing
+    anything to disk. The caller decides what to do with the result (BCC shows
+    the user the issues and asks before saving).
+
+    Returns (cfg, notes, repaired_text):
+      cfg           - the parsed dict from the repaired JSON
+      notes         - human-readable list of fixes that were applied
+      repaired_text - pretty-printed JSON the config would become
+
+    Raises ValueError if the file can't be salvaged automatically.
+    """
+    text = Path(path).read_text(encoding="utf-8")
+    candidate, notes = repair_json_text(text)
+    try:
+        obj = json.loads(candidate)
+    except json.JSONDecodeError as e:
+        raise ValueError(
+            f"Couldn't repair the file automatically (line {e.lineno}, column {e.colno}: {e.msg})."
+        ) from e
+    if not isinstance(obj, dict):
+        raise ValueError("Even after repair, the top level isn't a JSON object.")
+    pretty = json.dumps(obj, indent=2, ensure_ascii=False) + "\n"
+    return obj, notes, pretty
+
+
 def extract_servers(cfg: dict) -> list[ServerEntry]:
     """Pull enabled (`mcpServers`) and disabled (`_disabledMcpServers`) servers."""
     out: list[ServerEntry] = []