feat: lenient JSON repair for pasted MCP snippets

Pasted config snippets no longer have to be valid JSON. repair_json_text()
auto-fixes markdown fences, surrounding prose, // /* */ # comments,
trailing and missing commas, smart quotes, single quotes, unquoted keys,
Python/JS literals, and unclosed braces. parse_pasted_json_verbose()
reports every repair applied; the paste dialog now parses as you type
and previews exactly what will be added and what was fixed.

Also includes ruff lint fixes and formatting across bcc.py/bcc_core.py.

README.md

@@ -36,8 +36,12 @@ python bcc.py
   other file manually.
 - **Form-based editing** — name, command, args (one per line), env vars, or for
   remote servers: URL, transport, and headers. No raw JSON.
-- **Paste JSON** — drop in any snippet from an MCP doc (full `mcpServers` block,
-  inner map, or a single bare server object); it's parsed and merged.
+- **Paste JSON — even broken JSON** — drop in any snippet from an MCP doc (full
+  `mcpServers` block, inner map, or a single bare server object); it's parsed
+  and merged. The paste box parses as you type and auto-repairs the stuff docs
+  and chat windows love to break: markdown fences, surrounding prose, comments,
+  trailing or missing commas, smart quotes, single quotes, unquoted keys, and
+  unclosed braces — and tells you exactly what it fixed before you commit.
 - **Drag & drop** a `.json` file onto the window to import servers from it.
 - **Copy to ▸** — copy the selected server straight into your *other* install.
 - **Active / Disabled sections** — servers are shown in two labelled lists with