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)

2 files changed, 7 insertions, 3 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)."
diff --git a/wttrin.el b/wttrin.el
index 156b3b9..c0af306 100644
--- a/wttrin.el
+++ b/wttrin.el
@@ -35,7 +35,9 @@
 
 (require 'face-remap)
 (require 'url)
-(require 'xterm-color) ;; https://github.com/atomontage/xterm-color
+
+;; Declare xterm-color functions (loaded on-demand)
+(declare-function xterm-color-filter "xterm-color" (string))
 
 ;; Declare functions from wttrin-debug.el (loaded conditionally)
 (declare-function wttrin--debug-mode-line-info "wttrin-debug")
@@ -314,6 +316,7 @@ Return t if valid, nil if missing or contains errors."
 (defun wttrin--process-weather-content (raw-string)
   "Process RAW-STRING: apply ANSI filtering and remove verbose lines.
 Returns processed string ready for display."
+  (require 'xterm-color)
   (let ((processed (xterm-color-filter raw-string)))
     ;; Remove verbose Location: coordinate line
     (with-temp-buffer
@@ -347,6 +350,7 @@ Returns processed string ready for display."
       (let ((inhibit-read-only t))
         (erase-buffer)
         ;; Initialize xterm-color state AFTER wttrin-mode to prevent it being wiped
+        (require 'xterm-color)
         (setq-local xterm-color--state :char)
         (insert (wttrin--process-weather-content raw-string))
         (wttrin--add-buffer-instructions)