fix(tmux): parse macOS battery status

[ALX99]

Problem and impact

On macOS, the tmux status script rendered an empty battery percentage because its extended-regex parser used \d, which POSIX grep -E does not define as a digit class. It also matched charging inside discharging, so a low discharging battery could use the charging colour instead of the warning/critical colour.

Reproduction and observed result

Validated against untouched master commit 52ea8ecd508b4cb3cc529a3c6d3f69696cbf2060 with the exact current script in a fresh temporary Git repository. Temporary uname and pmset stubs selected the real Darwin branch and emitted standard battery rows.

With 12%; discharging, the parent printed:

#[fg=colour245]bat #[fg=colour75]%#[fg=default]

With 87%; charging, it also printed an empty percentage. Directly running the parent expression with GNU grep 3.11 produced no match for 87%.

Root cause and fix

The Darwin parser used grep -Eo "\d+%" and an unbounded case-insensitive search for charging.

The fix uses the portable ERE [0-9]+% and matches charging only as a complete semicolon/whitespace-delimited status word. Linux battery handling and status-line assembly are unchanged.

Validation commands and results

• bash -n .config/tmux/status — passed.
• Exact before/after harness with GNU Bash 5.2.37 and GNU grep 3.11:
  • 12%; discharging → 12% with the critical colour.
  • 87%; charging → 87% with the charging colour.
  • 100%; charged → 100% without being misclassified as charging.
• git diff --check — passed.
• Branch comparison to current master — one commit, zero commits behind, one modified file, two additions and two deletions.
• GitHub Linter workflow (ShellCheck across all shebang files) — passed.
• Local ShellCheck installation was also attempted through the approved internal Debian mirror, but the mirror returned HTTP 503; CI supplied the authoritative ShellCheck result.

Scope and risk

Only .config/tmux/status changes. No tests, configuration contracts, Linux behavior, generated files, dependencies, or unrelated code are modified. The risk is limited to parsing pmset -g batt text on macOS.