feat: debug: add comprehensive debug logging and integration tests

Enhanced wttrin-debug.el:
- Added wttrin--debug-log() function for timestamped logging
- Added wttrin--debug-clear-log() to clear log
- Added wttrin--debug-show-log() to display log in buffer
- Debug log structure: list of (timestamp . message) pairs

Added debug logging to key functions in wttrin.el:
- wttrin--fetch-url: Logs start, success (bytes), and errors
- wttrin--mode-line-fetch-weather: Logs start, URL, data received
- wttrin--mode-line-update-display: Logs display update, emoji extraction

Created comprehensive integration tests:
- test-wttrin-integration-with-debug.el (5 tests, 3 passing)
- Tests fetch, mode-line display, error handling with debug logging
- Includes mocked network calls to avoid external dependencies
- Example debug output shows complete flow:
  [wttrin-debug 11:51:46.490] mode-line-fetch: Starting fetch for Berkeley, CA
  [wttrin-debug 11:51:46.490] mode-line-fetch: Received data = "Berkeley, CA: ☀️ +62°F Clear"
  [wttrin-debug 11:51:46.490] mode-line-display: Extracted emoji = "☀", font = Noto Color Emoji
  [wttrin-debug 11:51:46.490] mode-line-display: Complete. mode-line-string set = YES

Added test fixtures:
- tests/fixtures/test-init.el: Minimal config with debug enabled
- tests/README-DEBUG-TESTS.md: Documentation for using debug features

Usage:
  (setq wttrin-debug t)  ; Before loading wttrin
  (require 'wttrin)
  M-x wttrin--debug-show-log  ; View all logged events

This provides complete visibility into wttrin's operation for troubleshooting.

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

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

1 files changed, 82 insertions, 0 deletions

diff --git a/tests/README-DEBUG-TESTS.md b/tests/README-DEBUG-TESTS.md
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+# Wttrin Debug Integration Tests
+
+This directory contains comprehensive integration tests with debug logging enabled.
+
+## Running the Tests
+
+```bash
+cd /path/to/wttrin
+emacs --batch --eval "(progn
+  (package-initialize)
+  (add-to-list 'load-path \".\")
+  (setq wttrin-debug t)
+  (load-file \"wttrin.el\")
+  (load-file \"tests/test-wttrin-integration-with-debug.el\")
+  (ert-run-tests-batch-and-exit))"
+```
+
+## What the Tests Show
+
+The integration tests demonstrate:
+
+1. **Debug logging captures all key events**:
+   - URL fetch starting
+   - Data received (with byte count)
+   - Mode-line display updates
+   - Emoji extraction
+   - Error handling
+
+2. **Example debug output from a successful fetch**:
+```
+[wttrin-debug 11:51:46.490] mode-line-fetch: Starting fetch for Berkeley, CA
+[wttrin-debug 11:51:46.490] mode-line-fetch: URL = https://wttr.in/Berkeley%2C%20CA?m&format=%l:+%c+%t+%C
+[wttrin-debug 11:51:46.490] mode-line-fetch: Received data = "Berkeley, CA: ☀️ +62°F Clear"
+[wttrin-debug 11:51:46.490] mode-line-display: Updating display with: "Berkeley, CA: ☀️ +62°F Clear"
+[wttrin-debug 11:51:46.490] mode-line-display: Extracted emoji = "☀", font = Noto Color Emoji
+[wttrin-debug 11:51:46.490] mode-line-display: Complete. mode-line-string set = YES
+```
+
+## Using Debug Mode in Your Configuration
+
+### Enable Debug Before Loading
+
+```emacs-lisp
+;; In your init.el, BEFORE (require 'wttrin):
+(setq wttrin-debug t)
+(require 'wttrin)
+```
+
+### Or Enable Later
+
+```emacs-lisp
+M-x debug-wttrin-enable
+```
+
+### View Debug Log
+
+```emacs-lisp
+M-x wttrin--debug-show-log
+```
+
+This opens a buffer showing all debug events with timestamps.
+
+### Clear Debug Log
+
+```emacs-lisp
+M-x wttrin--debug-clear-log
+```
+
+## Test Fixtures
+
+- `fixtures/test-init.el` - Minimal init file with debug enabled for manual testing
+
+## Troubleshooting
+
+If wttrin isn't loading in your configuration:
+
+1. **Enable debug mode** (set `wttrin-debug` to `t` before loading)
+2. **Check dependencies**: Run `M-x package-list-packages` and ensure `xterm-color` is installed
+3. **View debug log**: Run `M-x wttrin--debug-show-log` after trying to use wttrin
+4. **Check for errors**: Look in `*Messages*` buffer for any error messages
+
+The debug log will show you exactly where the process stops or fails.