feat(displays): hotplug auto-switch for display profiles (item 15b)

nomarchy-display-profile gains `match <outputs>`: an exact set match
wins, else the largest profile whose named outputs are all connected;
any tie prints nothing — the watcher must never flap between ambiguous
layouts. nomarchy-display-profile-watch (exec-once when profiles are
declared, the keyboard-watcher poll pattern — session units race
Hyprland IPC on relogin) reacts to output-set CHANGES only, reads
settings.displayProfileAuto from the live state each time (the menu's
new Auto-switch row toggles it instantly, no rebuild), and applies via
the tool — so an auto-pick persists a concrete profile that the next
rebuild bakes. A separate boolean rather than an "auto" pseudo-profile
for exactly that bake semantics.

Verified: V0 (flake check); V1 — a scratch 4-profile downstream builds;
tool + watcher pass bash -n; the match matrix exercised end-to-end:
three exact picks, an unambiguous-superset pick, a tie -> none, a
no-fit -> none; the watcher is exec-once'd in the rendered config; the
menu renders the Auto-switch row. Remains: V3 real dock/undock
(HARDWARE-QUEUE, rides the slice-a entry). Slice c (workspace binding)
stays, tagged optional.

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

agent/JOURNAL.md

@@ -17,6 +17,28 @@ Template:
 
 ---
 
+## 2026-07-05 — display profiles auto-switch (iteration #29, item 15b)
+- **Task:** BACKLOG NEXT#15 slice b — opt-in hotplug auto-switch.
+- **Did:** nomarchy-display-profile gains `match <outputs>` (exact set
+  → else unambiguous largest subset → ties/none = exit 1);
+  nomarchy-display-profile-watch polls `hyprctl monitors all` every 3s
+  (exec-once, the keyboard-watcher pattern — session units race
+  Hyprland IPC), reacts only to CHANGES, reads settings.displayProfileAuto
+  LIVE each change (instant menu toggle, no rebuild) and applies via
+  the tool, so auto-picks persist concrete profiles that rebuilds
+  bake. Chose a separate boolean over an "auto" pseudo-profile for
+  exactly that bake semantics. Menu: Auto-switch (on/off) row in
+  Profiles. Template + README notes.
+- **Verified:** V0; V1 — scratch 4-profile downstream builds; both
+  scripts bash -n; match matrix exercised: exact ×3, unambiguous
+  subset, tie → none, no-fit → none; watcher exec-once present; menu
+  renders with the row. Real hotplug needs a session+dock → V3 (rides
+  the slice-a queue entry).
+- **Pending:** V3. Slice c (workspace binding) remains, tagged
+  optional.
+- **Next suggestion:** #16 greeter theming — item 15's remaining
+  slice c is optional; a fresh item keeps variety.
+
 ## 2026-07-05 — display profiles slice a (iteration #28, item 15a)
 - **Task:** BACKLOG NEXT#15 slice a, per the #27 design: option +
   overlay + applier + menu + template example.