feat: add max_file_size preview limit and show_hidden_when_empty (#85)

* feat(preview): add `max_file_size` config to skip large file previews

Problem: previewing large files (e.g. 500 MB logs, binaries) loads them
into a buffer and can freeze or OOM Neovim. `disable_preview` only
receives the filename, so users cannot gate on file size.

Solution: add `preview_win.max_file_size` (number, MB, default 10). In
`open_preview`, check `entry.meta.stat.size` and fall back to
`vim.uv.fs_stat` when the cached stat is absent. If the file exceeds
the limit and a preview window is already open, render "File too large
to preview" in it; if not, emit a WARN notify and return early. The
cursor-moved auto-update path only fires when a window already exists,
so no flag threading is needed to distinguish explicit from implicit.

Based on: stevearc/oil.nvim#213

* feat(view): add `show_hidden_when_empty` for hidden-only directories

Problem: with `show_hidden = false`, a directory containing only
dotfiles renders as just `..`, giving no indication that entries exist.

Solution: add `view_options.show_hidden_when_empty` (boolean, default
false). After the main filter loop in `render_buffer`, if the option is
set and `#line_table <= 1`, iterate `entry_list` again and render any
entry not matched by `is_always_hidden`, using `is_hidden = true` so
they render with the dimmed hidden style.

Based on: stevearc/oil.nvim#473

* docs(upstream): fix formatting

* docs(upstream): update #213 and #473 with PR and commit links

lua/canola/config.lua

@@ -84,6 +84,7 @@ local default_config = {
   view_options = {
     -- Show files and directories that start with "."
     show_hidden = false,
+    show_hidden_when_empty = false,
     -- This function defines what is considered a "hidden" file
     is_hidden_file = function(name, bufnr)
       local m = name:match('^%.')
@@ -159,6 +160,7 @@ local default_config = {
     disable_preview = function(filename)
       return false
     end,
+    max_file_size = 10,
     -- Window-local options to use for preview window buffers
     win_options = {},
   },
@@ -306,6 +308,7 @@ local M = {}
 
 ---@class (exact) canola.ViewOptions
 ---@field show_hidden boolean
+---@field show_hidden_when_empty boolean
 ---@field is_hidden_file fun(name: string, bufnr: integer, entry: canola.Entry): boolean
 ---@field is_always_hidden fun(name: string, bufnr: integer, entry: canola.Entry): boolean
 ---@field natural_order boolean|"fast"
@@ -315,6 +318,7 @@ local M = {}
 
 ---@class (exact) canola.SetupViewOptions
 ---@field show_hidden? boolean Show files and directories that start with "."
+---@field show_hidden_when_empty? boolean When true and the directory has no visible entries, show hidden entries instead of an empty listing (:help canola.show_hidden_when_empty).
 ---@field is_hidden_file? fun(name: string, bufnr: integer): boolean This function defines what is considered a "hidden" file
 ---@field is_always_hidden? fun(name: string, bufnr: integer): boolean This function defines what will never be shown, even when `show_hidden` is set
 ---@field natural_order? boolean|"fast" Sort file names with numbers in a more intuitive order for humans. Can be slow for large directories.
@@ -371,6 +375,7 @@ local M = {}
 ---@field update_on_cursor_moved boolean
 ---@field preview_method canola.PreviewMethod
 ---@field disable_preview fun(filename: string): boolean
+---@field max_file_size number Maximum file size (in MB) to preview. Files larger than this will show a placeholder.
 ---@field win_options table<string, any>
 
 ---@class (exact) canola.ConfirmationWindowConfig : canola.WindowConfig
@@ -378,6 +383,7 @@ local M = {}
 ---@class (exact) canola.SetupPreviewWindowConfig
 ---@field update_on_cursor_moved? boolean Whether the preview window is automatically updated when the cursor is moved
 ---@field disable_preview? fun(filename: string): boolean A function that returns true to disable preview on a file e.g. to avoid lag
+---@field max_file_size? number Maximum file size in MB to show in preview. Files exceeding this will not be loaded (:help canola.preview_win). Set to nil to disable the limit.
 ---@field preview_method? canola.PreviewMethod How to open the preview window
 ---@field win_options? table<string, any> Window-local options to use for preview window buffers