feat(model): add model selection (#961)

* feat(model): add model selection with keybinding

* lint

* rename model_select to model_selector

lua/avante/model_selector.lua

@@ -0,0 +1,57 @@
+local Utils = require("avante.utils")
+local Config = require("avante.config")
+
+---@class avante.ModelSelector
+local M = {}
+
+---@param provider string
+---@param cfg table
+---@return table?
+local function create_model_entry(provider, cfg)
+  return cfg.model and {
+    name = provider .. "/" .. cfg.model,
+    provider = provider,
+    model = cfg.model,
+  }
+end
+
+function M.open()
+  local models = {}
+
+  -- Collect models from main providers and vendors
+  for _, provider in ipairs(Config.providers) do
+    local entry = create_model_entry(provider, Config.get_provider(provider))
+    if entry then table.insert(models, entry) end
+  end
+
+  for provider, cfg in pairs(Config.vendors or {}) do
+    if type(cfg) == "table" then
+      local entry = create_model_entry(provider, cfg)
+      if entry then table.insert(models, entry) end
+    end
+  end
+
+  if #models == 0 then
+    Utils.warn("No models available in config")
+    return
+  end
+
+  vim.ui.select(models, {
+    prompt = "Select Model:",
+    format_item = function(item) return item.name end,
+  }, function(choice)
+    if not choice then return end
+
+    -- Switch provider if needed
+    if choice.provider ~= Config.provider then require("avante.providers").refresh(choice.provider) end
+
+    -- Update config with new model
+    Config.override({
+      [choice.provider] = vim.tbl_deep_extend("force", Config.get_provider(choice.provider), { model = choice.model }),
+    })
+
+    Utils.info("Switched to model: " .. choice.name)
+  end)
+end
+
+return M