Add missing type specifications to improve type safety

- Add @spec annotations to all public functions in time_helpers.ex
- Add @spec annotations to all public functions in weather_units.ex
- Add @spec annotations to authentication functions in user_auth.ex
- Fix User struct type reference (use %Aprsme.Accounts.User{} instead of t())
- All dialyzer checks now pass successfully

These type specifications improve code documentation and enable better
compile-time type checking with dialyzer.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/aprsme/encoding_utils.ex

@@ -56,8 +56,6 @@ defmodule Aprsme.EncodingUtils do
   def to_float(value) when is_integer(value) do
     if value >= -9.0e15 and value <= 9.0e15 do
       value * 1.0
-    else
-      nil
     end
   end
 
@@ -77,7 +75,6 @@ defmodule Aprsme.EncodingUtils do
 
   def to_float(_), do: nil
 
-
   @doc """
   Converts various types to Decimal for database storage.
 

lib/aprsme_web/time_helpers.ex

@@ -7,6 +7,7 @@ defmodule AprsmeWeb.TimeHelpers do
   @doc """
   Returns a human-readable string for how long ago the given DateTime was.
   """
+  @spec time_ago_in_words(nil | NaiveDateTime.t() | DateTime.t()) :: String.t()
   def time_ago_in_words(nil), do: gettext("unknown time") <> " " <> gettext("ago")
 
   def time_ago_in_words(%NaiveDateTime{} = naive_datetime) do
@@ -42,6 +43,7 @@ defmodule AprsmeWeb.TimeHelpers do
   Handles ISO 8601 strings, Unix timestamps in milliseconds, and existing
   DateTime or NaiveDateTime structs.
   """
+  @spec to_datetime(String.t() | integer() | DateTime.t() | NaiveDateTime.t() | any()) :: DateTime.t() | nil
   def to_datetime(ts) do
     cond do
       is_binary(ts) ->

lib/aprsme_web/user_auth.ex

@@ -10,6 +10,8 @@ defmodule AprsmeWeb.UserAuth do
   # Make the remember me cookie valid for 60 days.
   # If you want bump or reduce this value, also change
   # the token expiry itself in UserToken.
+  alias Phoenix.LiveView.Socket
+
   @max_age 60 * 60 * 24 * 60
   @remember_me_cookie "_aprs_web_user_remember_me"
   @remember_me_options [sign: true, max_age: @max_age, same_site: "Lax"]
@@ -26,6 +28,7 @@ defmodule AprsmeWeb.UserAuth do
   disconnected on log out. The line can be safely removed
   if you are not using LiveView.
   """
+  @spec log_in_user(Plug.Conn.t(), %Aprsme.Accounts.User{}, map()) :: Plug.Conn.t()
   def log_in_user(conn, user, params \\ %{}) do
     token = Accounts.generate_user_session_token(user)
     user_return_to = get_session(conn, :user_return_to)
@@ -69,6 +72,7 @@ defmodule AprsmeWeb.UserAuth do
 
   It clears all session data for safety. See renew_session.
   """
+  @spec log_out_user(Plug.Conn.t()) :: Plug.Conn.t()
   def log_out_user(conn) do
     user_token = get_session(conn, :user_token)
     user_token && Accounts.delete_user_session_token(user_token)
@@ -87,6 +91,7 @@ defmodule AprsmeWeb.UserAuth do
   Authenticates the user by looking into the session
   and remember me token.
   """
+  @spec fetch_current_user(Plug.Conn.t(), any()) :: Plug.Conn.t()
   def fetch_current_user(conn, _opts) do
     {user_token, conn} = ensure_user_token(conn)
     user = user_token && Accounts.get_user_by_session_token(user_token)
@@ -144,6 +149,7 @@ defmodule AprsmeWeb.UserAuth do
         live "/profile", ProfileLive, :index
       end
   """
+  @spec on_mount(atom(), map(), map(), Socket.t()) :: {:cont | :halt, Socket.t()}
   def on_mount(:mount_current_user, _params, session, socket) do
     {:cont, mount_current_user(session, socket)}
   end
@@ -189,6 +195,7 @@ defmodule AprsmeWeb.UserAuth do
   @doc """
   Used for routes that require the user to not be authenticated.
   """
+  @spec redirect_if_user_is_authenticated(Plug.Conn.t(), any()) :: Plug.Conn.t()
   def redirect_if_user_is_authenticated(conn, _opts) do
     case conn.assigns[:current_user] do
       nil ->
@@ -207,6 +214,7 @@ defmodule AprsmeWeb.UserAuth do
   If you want to enforce the user email is confirmed before
   they use the application at all, here would be a good place.
   """
+  @spec require_authenticated_user(Plug.Conn.t(), any()) :: Plug.Conn.t()
   def require_authenticated_user(conn, _opts) do
     case conn.assigns[:current_user] do
       nil ->

lib/aprsme_web/weather_units.ex

@@ -10,6 +10,7 @@ defmodule AprsmeWeb.WeatherUnits do
   Determines the unit system based on locale.
   Returns :imperial for US, :metric for most other countries.
   """
+  @spec unit_system(String.t() | nil | any()) :: :imperial | :metric
   def unit_system(locale) when is_binary(locale) do
     case locale do
       # Default to imperial for English
@@ -32,6 +33,7 @@ defmodule AprsmeWeb.WeatherUnits do
   Converts temperature from Fahrenheit to Celsius if needed.
   Returns the temperature in the appropriate unit for the locale.
   """
+  @spec format_temperature(number() | any(), String.t()) :: {number() | any(), String.t()}
   def format_temperature(temp, locale) when is_number(temp) do
     case unit_system(locale) do
       :imperial -> {temp, "°F"}
@@ -45,6 +47,7 @@ defmodule AprsmeWeb.WeatherUnits do
   Converts wind speed from mph to km/h if needed.
   Returns the wind speed in the appropriate unit for the locale.
   """
+  @spec format_wind_speed(number() | any(), String.t()) :: {number() | any(), String.t()}
   def format_wind_speed(speed, locale) when is_number(speed) do
     case unit_system(locale) do
       :imperial -> {speed, "mph"}
@@ -58,6 +61,7 @@ defmodule AprsmeWeb.WeatherUnits do
   Converts rain from inches to mm if needed.
   Returns the rain amount in the appropriate unit for the locale.
   """
+  @spec format_rain(number() | any(), String.t()) :: {number() | any(), String.t()}
   def format_rain(rain, locale) when is_number(rain) do
     case unit_system(locale) do
       :imperial -> {rain, "in"}
@@ -70,6 +74,7 @@ defmodule AprsmeWeb.WeatherUnits do
   @doc """
   Formats pressure (keeps hPa for all locales as it's standard).
   """
+  @spec format_pressure(number() | any(), any()) :: {number() | any(), String.t()}
   def format_pressure(pressure, _locale) when is_number(pressure) do
     {pressure, "hPa"}
   end
@@ -79,6 +84,12 @@ defmodule AprsmeWeb.WeatherUnits do
   @doc """
   Gets the appropriate unit labels for the locale.
   """
+  @spec unit_labels(String.t()) :: %{
+          temperature: String.t(),
+          wind_speed: String.t(),
+          rain: String.t(),
+          pressure: String.t()
+        }
   def unit_labels(locale) do
     case unit_system(locale) do
       :imperial ->