refactor: core: lazy-load xterm-color dependency

Move xterm-color from top-level require to on-demand loading within
functions that actually use it. This simplifies user configuration
by eliminating the need for separate xterm-color use-package declarations.

Changes:
- Replace top-level (require 'xterm-color) with declare-function
- Add (require 'xterm-color) in wttrin--process-weather-content
- Add (require 'xterm-color) in wttrin--display-weather
- Update smoke test to check loadability vs. feature presence

Benefits:
- Simpler use-package config (no :after xterm-color needed)
- xterm-color still auto-installed via Package-Requires on MELPA
- Load time optimization (loads only when displaying weather)

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/test-wttrin-smoke.el b/tests/test-wttrin-smoke.el
index 5cb4b08..acf7fd5 100644
--- a/tests/test-wttrin-smoke.el
+++ b/tests/test-wttrin-smoke.el
@@ -33,9 +33,9 @@ If we got here, the package loaded successfully via (require 'wttrin)."
 ;;; Dependency Tests
 
 (ert-deftest test-wttrin-smoke-xterm-color-available ()
-  "Test that xterm-color dependency is available.
+  "Test that xterm-color dependency can be loaded when needed.
 This is a REQUIRED dependency - wttrin cannot function without it."
-  (should (featurep 'xterm-color)))
+  (should (require 'xterm-color nil t)))
 
 (ert-deftest test-wttrin-smoke-url-available ()
   "Test that url library is available (built-in)."