feat: implement user-defined text shortcuts (#2512)

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

lua/cmp_avante/shortcuts.lua

@@ -0,0 +1,51 @@
+local api = vim.api
+
+---@class ShortcutsSource : cmp.Source
+local ShortcutsSource = {}
+ShortcutsSource.__index = ShortcutsSource
+
+function ShortcutsSource:new()
+  local instance = setmetatable({}, ShortcutsSource)
+  return instance
+end
+
+function ShortcutsSource:is_available() return vim.bo.filetype == "AvanteInput" end
+
+function ShortcutsSource.get_position_encoding_kind() return "utf-8" end
+
+function ShortcutsSource:get_trigger_characters() return { "#" } end
+
+function ShortcutsSource:get_keyword_pattern() return [[\%(@\|#\|/\)\k*]] end
+
+function ShortcutsSource:complete(_, callback)
+  local Utils = require("avante.utils")
+  local kind = require("cmp").lsp.CompletionItemKind.Variable
+  local shortcuts = Utils.get_shortcuts()
+
+  local items = {}
+  for _, shortcut in ipairs(shortcuts) do
+    table.insert(items, {
+      label = "#" .. shortcut.name,
+      kind = kind,
+      detail = shortcut.details,
+      data = {
+        name = shortcut.name,
+        prompt = shortcut.prompt,
+        details = shortcut.details,
+      },
+    })
+  end
+
+  callback({
+    items = items,
+    isIncomplete = false,
+  })
+end
+
+function ShortcutsSource:execute(item, callback)
+  -- ShortcutsSource should only provide completion, not perform replacement
+  -- The actual shortcut replacement is handled in sidebar.lua handle_submit function
+  callback()
+end
+
+return ShortcutsSource