feat: Fix modeline lag and add org multi-level sort with comprehensive tests

Performance improvement and new feature with full test coverage.

## Changes

### 1. Fix modeline line/column position lag (#A priority)
- Replace expensive line-number-at-pos with cached %l/%c format specifiers
- Enable line-number-mode explicitly for caching
- Result: Instant modeline updates, zero performance overhead
- Files: modules/modeline-config.el:81-83, modules/ui-config.el:53

### 2. Implement multi-level org sorting
- New function: cj/org-sort-by-todo-and-priority
- Sorts by TODO status (TODO before DONE) AND priority (A→B→C→D)
- Uses stable sorting: priority first, then TODO state
- Gracefully handles empty sections (no error)
- Bound to C-; o o (ordering → org sort)
- Files: modules/org-config.el:278-299, modules/custom-ordering.el:253,267

### 3. Comprehensive ERT test suite (12/12 passing)
- Normal cases: Mixed TODO/DONE, multiple of same type, same priority
- Boundary cases: Empty sections, single entries, no priorities
- Error cases: Non-org-mode buffer
- Test file: tests/test-org-sort-by-todo-and-priority.el

### 4. Testing improvements discovered
- Disable org-mode hooks to avoid package dependencies in batch mode
- org-sort-entries must be called from parent heading
- Preserve priority cookie in org-get-heading (t t nil t)
- Add condition-case to handle "Nothing to sort" gracefully

### 5. Minor cleanup
- Comment out chime-debug setting (org-agenda-config.el:267)
- Mark modeline lag task as DONE in todo.org

## Technical Details

Modeline optimization:
- line-number-at-pos is O(n) where n = current line
- %l and %c are O(1) lookups from cached values

Org sorting algorithm uses stable sort:
1. Sort by priority (A, B, C, D, unprioritized)
2. Sort by TODO status (preserves priority order within groups)
Result: TODO [#A], TODO [#B], DONE [#A], DONE [#B], etc.

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

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

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