feat: Add LanguageTool integration for comprehensive grammar checking

Integrated LanguageTool as an on-demand grammar checker, replacing the
previously disabled proselint checker.

Changes:
- Created scripts/languagetool-flycheck wrapper for flycheck integration
  - Converts LanguageTool JSON output to flycheck format
  - Includes suggestions in error messages
  - 30-second timeout for large files

- Updated modules/flycheck-config.el:
  - Defined languagetool checker for text/markdown/org/gfm modes
  - Updated cj/flycheck-prose-on-demand to use LanguageTool
  - Added installation instructions (sudo pacman -S languagetool)
  - Improved documentation clarity

- Usage: Press C-; ? in org/text/markdown files
  - Enables flycheck with LanguageTool
  - Shows errors in *Flycheck errors* buffer
  - On-demand only (no performance impact)

- Updated docs/NOTES.org:
  - Added best practice: Test Emacs launch after non-trivial changes
  - Example: emacs --eval "(kill-emacs)"
  - Catches startup errors before committing

- Disabled weather debug mode (wttrin-debug nil)

- Marked todo.org grammar checker task as DONE

LanguageTool catches real grammar issues (subject-verb agreement, tense,
punctuation, common mistakes) that proselint missed.

Installation: LanguageTool 6.6 (222MB) from Arch repos
Dependencies: Python 3 (for wrapper script)

1 files changed, 20 insertions, 3 deletions

diff --git a/todo.org b/todo.org
index 3641c912..126dc62f 100644
--- a/todo.org
+++ b/todo.org
@@ -204,9 +204,26 @@ Use M-x profiler-start before Method 3 debug-profiling.el is built.
 15-20 seconds every time capturing a task (12+ times/day).
 Major daily bottleneck - minutes lost waiting, plus context switching cost.
 
-** TODO [#C] Fix grammar checker performance (currently disabled)
-
-Currently disabled because it breaks flow when writing.
+** DONE [#C] Fix grammar checker performance (currently disabled)
+CLOSED: [2025-11-04 Mon]
+
+✅ **Installed and configured LanguageTool for comprehensive grammar checking**
+
+Replaced disabled grammar checker with on-demand LanguageTool integration:
+- Installed LanguageTool 6.6-2 from Arch repos (222MB)
+- Created wrapper script: scripts/languagetool-flycheck (Python 3)
+- Integrated with flycheck for on-demand checking via C-; ?
+- Removed proselint (redundant - LanguageTool catches more)
+- No performance impact: only runs when explicitly invoked
+- Installation instructions added to modules/flycheck-config.el commentary
+
+LanguageTool catches:
+- Real grammar errors (subject-verb agreement, tense, etc.)
+- Missing punctuation (commas, periods)
+- Common mistakes (could of → could have)
+- Style issues (redundant phrases, wordiness)
+
+Workflow: Open org/text/markdown file → press C-; ? → see errors in *Flycheck errors* buffer
 
 ** TODO [#D] Fix EMMS keybinding inconsistency with other buffers