refactor: add typespecs and module constants

- Add @spec for public functions in Member and UserLive.Form
- Replace magic numbers with module constants:
  - @member_search_limit = 10
  - @default_similarity_threshold = 0.2
- Add comprehensive @doc for filter_by_email_match and fuzzy_search

lib/membership/member.ex

@@ -38,6 +38,10 @@ defmodule Mv.Membership.Member do
   require Ash.Query
   import Ash.Expr
 
+  # Module constants
+  @member_search_limit 10
+  @default_similarity_threshold 0.2
+
   postgres do
     table "members"
     repo Mv.Repo
@@ -152,9 +156,10 @@ defmodule Mv.Membership.Member do
       prepare fn query, _ctx ->
         q = Ash.Query.get_argument(query, :query) || ""
 
-        # 0.2 as similarity threshold (recommended)
-        # Lower value can lead to more results but also to more unspecific results
-        threshold = Ash.Query.get_argument(query, :similarity_threshold) || 0.2
+        # Use default similarity threshold if not provided
+        # Lower value leads to more results but also more unspecific results
+        threshold =
+          Ash.Query.get_argument(query, :similarity_threshold) || @default_similarity_threshold
 
         if is_binary(q) and String.trim(q) != "" do
           q2 = String.trim(q)
@@ -226,28 +231,58 @@ defmodule Mv.Membership.Member do
                 fragment("? % first_name", ^trimmed) or
                 fragment("? % last_name", ^trimmed) or
                 fragment("word_similarity(?, first_name) > 0.2", ^trimmed) or
-                fragment("word_similarity(?, last_name) > 0.2", ^trimmed) or
-                fragment("similarity(first_name, ?) > 0.2", ^trimmed) or
-                fragment("similarity(last_name, ?) > 0.2", ^trimmed) or
+                fragment(
+                  "word_similarity(?, last_name) > ?",
+                  ^trimmed,
+                  ^@default_similarity_threshold
+                ) or
+                fragment(
+                  "similarity(first_name, ?) > ?",
+                  ^trimmed,
+                  ^@default_similarity_threshold
+                ) or
+                fragment("similarity(last_name, ?) > ?", ^trimmed, ^@default_similarity_threshold) or
                 contains(email, ^trimmed)
             )
           )
-          |> Ash.Query.limit(10)
+          |> Ash.Query.limit(@member_search_limit)
         else
           # No search query: return all unlinked members
           # Caller should use filter_by_email_match helper for email match logic
           base_query
-          |> Ash.Query.limit(10)
+          |> Ash.Query.limit(@member_search_limit)
         end
       end
     end
   end
 
-  # Public helper function to apply email match logic after query execution
-  # This should be called after using :available_for_linking with user_email argument
-  #
-  # If a member with matching email exists, returns only that member
-  # Otherwise returns all members (no filtering)
+  @doc """
+  Filters members list to return only email match if exists.
+
+  If a member with matching email exists in the list, returns only that member.
+  Otherwise returns all members unchanged (no filtering).
+
+  This is typically used after calling `:available_for_linking` action with
+  a user_email argument to apply email-match priority logic.
+
+  ## Parameters
+    - `members` - List of Member structs to filter
+    - `user_email` - Email string to match against member emails
+
+  ## Returns
+    - List of Member structs (either single match or all members)
+
+  ## Examples
+
+      iex> members = [%Member{email: "test@example.com"}, %Member{email: "other@example.com"}]
+      iex> filter_by_email_match(members, "test@example.com")
+      [%Member{email: "test@example.com"}]
+
+      iex> filter_by_email_match(members, "nomatch@example.com")
+      [%Member{email: "test@example.com"}, %Member{email: "other@example.com"}]
+
+  """
+  @spec filter_by_email_match([t()], String.t()) :: [t()]
   def filter_by_email_match(members, user_email)
       when is_list(members) and is_binary(user_email) do
     # Check if any member matches the email
@@ -262,6 +297,7 @@ defmodule Mv.Membership.Member do
     end
   end
 
+  @spec filter_by_email_match(any(), any()) :: any()
   def filter_by_email_match(members, _user_email), do: members
 
   validations do
@@ -436,7 +472,32 @@ defmodule Mv.Membership.Member do
     identity :unique_email, [:email]
   end
 
-  # Fuzzy Search function that can be called by live view and calls search action
+  @doc """
+  Performs fuzzy search on members using PostgreSQL trigram similarity.
+
+  Wraps the `:search` action with convenient opts-based argument passing.
+  Searches across first_name, last_name, email, and other text fields using
+  full-text search combined with trigram similarity.
+
+  ## Parameters
+    - `query` - Ash.Query.t() to apply search to
+    - `opts` - Keyword list or map with search options:
+      - `:query` or `"query"` - Search string
+      - `:fields` or `"fields"` - Optional field restrictions
+
+  ## Returns
+    - Modified Ash.Query.t() with search filters applied
+
+  ## Examples
+
+      iex> Member |> fuzzy_search(%{query: "Greta"}) |> Ash.read!()
+      [%Member{first_name: "Greta", ...}]
+
+      iex> Member |> fuzzy_search(%{query: "gre"}) |> Ash.read!()  # typo-tolerant
+      [%Member{first_name: "Greta", ...}]
+
+  """
+  @spec fuzzy_search(Ash.Query.t(), keyword() | map()) :: Ash.Query.t()
   def fuzzy_search(query, opts) do
     q = (opts[:query] || opts["query"] || "") |> to_string()