fix: deferred dep loading + idempotent setup

Two related bugs surfaced when the user tried adding `setup({...})` to
their init.lua alongside our auto-setup:

1. **`inmemory.bps = nil` crash.** When a user's `init.lua` does
   `vim.pack.add(..., turbo-debug)` and then calls `setup({...})`
   synchronously right after, the nested `vim.pack.add` calls inside
   our own `plugin/turbo-debug.lua` (for dap/dapui/persistent-
   breakpoints) are DEFERRED by nvim's pack module — so the user's
   follow-up `require('persistent-breakpoints')` throws "module not
   found". On the previous `initialized = true` guard, the error set
   the flag but left setup half-complete; any later call short-
   circuited and `inmemory.bps` stayed `nil`, exploding the first
   breakpoint toggle (`api.lua:15: attempt to index field 'bps'`).

2. **Colorscheme override ignored.** Same root cause: user's
   `setup({ colorscheme = "nightfox" })` errored before reaching
   `config.merge`, so `config.opts.colorscheme` stayed `nil` and
   `M.enter` never switched themes.

Three changes that together fix both:

- **`init.lua` `setup()` self-defers** when `require('persistent-
  breakpoints')` fails, `vim.schedule`s itself once deps can load.
- **`plugin/turbo-debug.lua` auto-setup is now `vim.schedule`d** and
  skips entirely if the user's explicit `setup({...})` already ran
  (tracked via `M._setup_called`) — no more stomping user opts with
  a second `config.merge(nil)`.
- **`breakpoints.setup` is now fully idempotent**: dropped the
  `initialized` flag, since every call inside it
  (`persistent-breakpoints.setup`, `sign_define`, `nvim_set_hl`,
  `vim.keymap.set`) is safe to re-run.

lua/turbo-debug/breakpoints.lua

@@ -2,12 +2,26 @@ local config = require("turbo-debug.config")
 
 local M = {}
 
-local initialized = false
-
+-- This function is idempotent — every operation inside is safe to re-run.
+-- That property matters because turbo-debug.setup() can get called twice in
+-- practice:
+--   (1) Deferred auto-setup from plugin/turbo-debug.lua, which runs after
+--       vim.pack.add has finished registering all deps in runtimepath. The
+--       defer is necessary — calling setup synchronously during
+--       vim.pack.add would try to `require('persistent-breakpoints.api')`
+--       before the plugin's lua/ directory is on the runtimepath and
+--       crash with "module not found".
+--   (2) User's explicit setup({...}) in their init.lua with config
+--       overrides. It runs immediately (before the deferred auto-setup).
+--
+-- Previously a single `initialized` flag guarded this function so it only
+-- ran once. That guard was fragile: if the first call errored partway
+-- (case above), the flag was set but the setup was incomplete, and the
+-- second call skipped the retry. We now let every call do its full work;
+-- persistent-breakpoints.setup re-reads its bps file, sign_define overrides
+-- a previous definition, nvim_set_hl overrides a previous link, and
+-- vim.keymap.set overrides a previous binding.
 function M.setup()
-  if initialized then return end
-  initialized = true
-
   require("persistent-breakpoints").setup({
     load_breakpoints_event = { "BufReadPost" },
   })

lua/turbo-debug/init.lua

@@ -4,6 +4,21 @@ local mode = require("turbo-debug.mode")
 local M = {}
 
 function M.setup(opts)
+  -- Self-defer if dependencies aren't yet on the runtimepath. This happens
+  -- when the user calls `setup({...})` from their init.lua right after
+  -- `vim.pack.add(..., turbo-debug)`: our plugin/turbo-debug.lua fires
+  -- nested `vim.pack.add` calls for dap/dapui/persistent-breakpoints, but
+  -- those nested adds only register the paths on the NEXT event loop tick
+  -- — so a synchronous follow-up `require('persistent-breakpoints')`
+  -- crashes with "module not found". `vim.schedule` lets the pack module
+  -- finalize before we retry. `_setup_called` still gets set on the retry,
+  -- so plugin/turbo-debug.lua's own deferred auto-setup correctly skips.
+  if not pcall(require, "persistent-breakpoints") then
+    vim.schedule(function() M.setup(opts) end)
+    return
+  end
+
+  M._setup_called = true
   config.merge(opts)
   require("turbo-debug.breakpoints").setup()
   require("turbo-debug.adapters").setup()