Fix invisible/flashing clock, map Protect's 8-camera preset, warn on gaps

Three separate faults made cameras "not load" and the clock misbehave.

Clock rendered as nothing, or flashed ~200ms/second. The time was drawn as
an ASS osd-overlay pushed over mpv IPC, but on mpv 0.35 + Mesa/V3D + sway an
OSD overlay is rendered only on the frame where its content *changes*. Every
layer reports success while this happens (mpv returns error:success,
vo-configured is true, and sway reports the window visible at the right
rect), so it looks like a stacking or font bug and is neither. Ruled out:
pushing at 20Hz (identical content is ignored, so it still only redrew when
the second flipped), osd-msg1, show-text, and --pause (mpv stops redrawing
entirely). Fonts were never the issue.

The time is now baked into every frame by a drawtext filter re-reading a
small file the ticker rewrites once a second, with two constraints that cost
real time to find and are pinned by tests:

- The canvas alpha must be > 0. A fully transparent canvas (black@0.0 with
  --alpha=yes) makes the glyphs inherit alpha 0 and the compositor draws
  nothing -- this was the original invisible clock. New clock
  background_opacity (default 0.45) is clamped in config *and* in args() so
  no code path can produce an invisible clock.
- Readahead must be off. drawtext stamps the time when a frame is
  *generated*, so buffering ahead makes the visible clock lag by the
  readahead and swallows text-file updates entirely.

Since the text now arrives through a file, the clock needs no IPC socket:
dropped --input-ipc-server, the ipcPath field, and the stale-socket removal.
assEscape goes with the ASS path.

`views import` produced layouts with holes. viewmap derived the grid from
the slot count alone and ignored Protect's `layout` field, so Protect's
asymmetric 8-camera preset (four 2x2 tiles plus a right column of four 1x1)
landed as 8 tiles in a 3x3 grid -- the bottom-right cell was simply empty
and rendered as a blank rectangle. That preset is now mapped exactly; other
counts keep the uniform GridForSlots fallback rather than guessing at
presets I have not observed. Import also warns when a mapping would leave
empty cells or references a camera missing from the config, so a silent hole
cannot reach the screen again.

Also:

- clock.corner gains bottom-center and top-center (centered horizontally,
  Margin still applies vertically).
- placeClock no longer re-issues `resize set` every tick. Re-asserting
  geometry on a correctly-sized window makes sway send a configure event,
  which makes mpv reallocate buffers and blank for a frame. New
  compositor.Raise re-asserts z-order only, which is all the 2s tick needs;
  geometry is re-placed only when it has actually drifted.
- README documents why the clock is drawn this way, the preset table and how
  to add another from `views dump`, and three troubleshooting entries for
  failure modes that all look like bugs: a blank tile whose mpv is running
  (a stale camera entry -- re-adopting a camera in Protect assigns a new id
  and often a slightly different name, and `discover` never prunes), cameras
  in `cameras:` not being on screen (only the active layout's tiles stream),
  and black bars inside tiles (non-16:9 grid cells; --panscan=1.0 crops to
  fill instead).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LYhTnkp7VzJ67THeicgfAQ

internal/daemon/daemon.go

@@ -170,13 +170,29 @@ func (d *Daemon) placeClock(ctx context.Context, clock *player.Clock, rect compo
 		if pid == 0 {
 			continue
 		}
+		// Only re-assert geometry when it has actually drifted. Sending
+		// `resize set` every tick makes sway reconfigure the surface, which
+		// blanks mpv for a frame and reads as a flashing clock. Z-order still
+		// needs re-asserting every tick, because a restarted camera maps
+		// focused and lands above the overlay — but a bare focus does not
+		// touch the surface.
+		if rects, err := d.comp.WindowRects(ctx); err == nil {
+			if actual, ok := rects[pid]; ok && actual == rect {
+				if err := d.comp.Raise(ctx, pid); err != nil {
+					d.log.Debug("clock raise failed", "err", err)
+				}
+				continue
+			}
+		}
 		if err := d.comp.PlaceAndRaise(ctx, pid, rect); err != nil {
 			d.log.Debug("clock place failed", "err", err)
 		}
 	}
 }
 
-// clockRect computes the overlay rectangle for the configured corner.
+// clockRect computes the overlay rectangle for the configured corner. The
+// *-center positions are horizontally centred on the output, which is why the
+// setting is a position rather than strictly a corner.
 func clockRect(w, h int, cl config.Clock) compositor.Rect {
 	m, cw, ch := cl.Margin, cl.Width, cl.Height
 	x, y := w-cw-m, h-ch-m // bottom-right default
@@ -187,6 +203,10 @@ func clockRect(w, h int, cl config.Clock) compositor.Rect {
 		x, y = m, m
 	case "top-right":
 		x, y = w-cw-m, m
+	case "bottom-center":
+		x, y = (w-cw)/2, h-ch-m
+	case "top-center":
+		x, y = (w-cw)/2, m
 	}
 	return compositor.Rect{X: x, Y: y, W: cw, H: ch}
 }