Add split-wezterm: split WezTerm pane into a rows x cols grid

Splits the current pane into evenly-sized grid using wezterm cli
split-pane. Supports optional command per pane, dryrun mode, and
auto-detects native or Flatpak WezTerm CLI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test-split-wezterm.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+SCRIPT="$(cd "$(dirname "$0")/.." && pwd)/scripts/split-wezterm"
+PASS=0; FAIL=0
+
+pass() { echo -e "\e[32m  PASS\e[0m $1"; (( PASS++ )); }
+fail() { echo -e "\e[31m  FAIL\e[0m $1: $2"; (( FAIL++ )); }
+
+assert_exit() {
+    local desc="$1" expected="$2"; shift 2
+    local actual
+    "$@" >/dev/null 2>&1 && actual=0 || actual=$?
+    if [[ "$actual" == "$expected" ]]; then pass "$desc"; else fail "$desc" "expected exit $expected, got $actual"; fi
+}
+
+assert_output_contains() {
+    local desc="$1" pattern="$2"; shift 2
+    local output
+    output=$("$@" 2>&1) || true
+    if echo "$output" | grep -qF "$pattern"; then pass "$desc"; else fail "$desc" "output missing: $pattern"; fi
+}
+
+assert_line_count() {
+    local desc="$1" expected="$2"; shift 2
+    local count
+    count=$("$@" 2>&1 | grep -c '^\[dryrun\]') || true
+    if [[ "$count" == "$expected" ]]; then pass "$desc"; else fail "$desc" "expected $expected dryrun lines, got $count"; fi
+}
+
+export WEZTERM_PANE=0
+
+echo "=== split-wezterm tests ==="
+
+# Help
+assert_exit "help flag exits 0" 0 "$SCRIPT" --help
+assert_output_contains "help shows usage" "Usage:" "$SCRIPT" --help
+
+# Validation
+assert_exit "no args exits 1" 1 "$SCRIPT"
+assert_exit "one arg exits 1" 1 "$SCRIPT" 3
+assert_exit "zero rows exits 1" 1 "$SCRIPT" 0 3
+assert_exit "rows > 10 exits 1" 1 "$SCRIPT" 11 3
+assert_exit "non-integer rows exits 1" 1 "$SCRIPT" abc 3
+
+# 1x1 — no-op
+assert_exit "1x1 exits 0" 0 "$SCRIPT" 1 1
+assert_output_contains "1x1 says nothing to do" "nothing to do" "$SCRIPT" 1 1
+
+# Dryrun counts (each split-pane = 1 dryrun line + 1 summary line)
+# 2x1 = 1 row split + 1 summary = 2 lines
+assert_line_count "2x1 produces 1 split" 2 "$SCRIPT" --dryrun 2 1
+# 1x3 = 2 col splits + 1 summary = 3 lines
+assert_line_count "1x3 produces 2 splits" 3 "$SCRIPT" --dryrun 1 3
+# 2x2 = 1 row + 2 col + 1 summary = 4 lines
+assert_line_count "2x2 produces 3 splits" 4 "$SCRIPT" --dryrun 2 2
+# 3x4 = 2 row + 9 col + 1 summary = 12 lines
+assert_line_count "3x4 produces 11 splits" 12 "$SCRIPT" --dryrun 3 4
+# 3x4 with command = 11 splits + 1 send-text + 1 summary = 13 lines
+assert_line_count "3x4 with cmd produces 13 lines" 13 "$SCRIPT" --dryrun 3 4 -- echo hi
+
+# Summary line
+assert_output_contains "dryrun summary" "Would create 3x4 grid (12 panes)" "$SCRIPT" --dryrun 3 4
+
+echo ""
+echo "Results: $PASS passed, $FAIL failed"
+(( FAIL == 0 ))