feat(bar): timezone line in the clock tooltip (LATER item)

Hovering the clock now leads with the zone — "{:%Z (UTC%z)}" above the
calendar — on the generated bar and both summer whole-swaps (parity).
Under auto-timezone the existing tz-watch SIGUSR2 reload keeps it
showing the currently detected zone. %Z is the abbreviation (BST), not
the IANA name — strftime has no code for that, and it satisfies the
"(optional)" nicety.

Verified: V0; V1 — the rendered generated config carries the new
tooltip-format and both summer jsonc parse with it. Hover render
queued for hardware.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -234,7 +234,6 @@ them as composable commands, not dead ends.
 - **Night-light geo mode**: lat/long auto sunset/sunrise (means wlsunset).
 - **Per-theme icon overrides** / more icon packs (ROADMAP § Icon themes).
 - **MIPI/IPU software-ISP camera** support (no-UVC machines).
-- **Auto-timezone Waybar tooltip** showing the detected zone (optional).
 - **VPN exit-node richer display** (country/city) (optional).
 - **NixOS release bump → v2** `[human]`: deliberate, hand-edited, never
   automated; the previous attempt was discarded (2026-06-22) over a