Add Claude Code hooks, commands, and permissions

High priority:

- Auto-format on edit (.claude/hooks/format-elixir.sh): runs mix format
  synchronously after every Edit/Write on .ex, .exs, and .heex files.
  Ensures code is formatted before the next read or tool call.

- mix test permissions: added Bash(mix test) (bare) and Bash(mix test *)
  (with path/flags) to the allow list. Previously only Bash(mix test:*)
  was allowed, which didn't match common invocations.

- Slash commands: /precommit runs the full mix precommit pipeline and
  reports failures with fix suggestions. /oban-status queries Oban job
  state via Tidewave SQL, grouped by state and worker.

Medium priority:

- Chrome DevTools permissions: added 8 new tools (select_page,
  list_network_requests, get_network_request, list_console_messages,
  get_console_message, hover, press_key, wait_for) for debugging API
  traffic, JS hook errors, hover states, and keyboard navigation.

- Gettext extraction hook (.claude/hooks/gettext-extract.sh): runs
  mix gettext.extract --merge asynchronously after editing .heex files.
  Async because it's project-wide and doesn't need to block the next edit.

- Sobelow permission: added Bash(mix sobelow:*) to the allow list for
  independent security checks.

mix.exs

@@ -161,7 +161,10 @@ defmodule MusicLibrary.MixProject do
       ],
       "ecto.setup": ["ecto.create", "ecto.migrate"],
       "ecto.reset": ["ecto.drop", "ecto.setup"],
-      shellcheck: "cmd fd . 'scripts/' --exclude '*.hurl' -t file --exec shellcheck --color",
+      shellcheck: [
+        "cmd fd . 'scripts/' --exclude '*.hurl' -t file --exec shellcheck --color",
+        "cmd fd . '.claude/hooks' -t file --exec shellcheck --color"
+      ],
       lint: [
         "format",
         "credo",