feat(client): T-1153 + T-1152 client half — continuous cursor-anchored zoom ladder, Region-rung orbital entry, click-through retired

The atlas 'regional' screen now opens the LADDER at the canonical orbital
frame (Region granularity, whole body fitted and centered) and wheel zoom
descends continuously — cursor-anchored, unclamped across rungs, with
progressive refinement (held composite keeps drawing, finer rung swaps in
place on arrival; no blank frame, no mode flip). Full-zoom-out resets to
the canonical planetary frame per Jeroen's HARD condition
(is_fully_zoomed_out = extent >= body circumference, not a zoom-value
heuristic). The district_screen nav hop is deleted — D-013 restored:
descent is a zoom gesture, not a nav push. AtlasViewer's heightmap-texture
path is unreachable from nav (code intact; overlay surface deferred, see
report/tickets).

Rung selection: design doc §5's literal formula has NO legal District band
at any real viewport (visual-tolerance band and n=64 coverage ceiling
never overlap — pinned by executable boundary tests at 1600x900);
select_rung() splits it into a coverage ceiling (decides Region) then the
2x visual tolerance (District vs Quarter), documented at the function.
In practice the ladder steps Region -> Quarter directly.

Wire: window_granularity_v2 encoded (omitted at District for byte-compat),
granularity_v2 echoed value keyed + staleness-guarded end to end; Region
clamp mirror replicates the server's bounded halving loop (no closed
form). MIN/MAX_ZOOM widened to [0.0005, 64] — the old 0.5 floor would
have clamped a real body's canonical fit zoom, violating the reset
condition.

Real pre-existing bug fixed in atlas_window_overlay.gd: the draw path used
echoed n as both cell-grid dimension and district extent — only
coincidentally correct at District granularity; Quarter/Region would have
read wrong array offsets. cell_grid_side_for_window() now mirrors the
server's WindowGranularity::cell_grid_side.

Tests: +26 pure-function geometry tests, new 30-test zoom-ladder suite,
extensions across the window cache/request/overlay/delivery suites.
Full suite 3518 green; cold-parse clean.

client/scripts/protocol/protocol.gd

@@ -782,16 +782,27 @@ static func encode_request_bookmark_catalog() -> PackedByteArray:
 ## Omitted callers (every whole-body-layer call site predating T-1138) are
 ## byte-unchanged. window_granularity/window_min_wl_m (T-1150): same
 ## byte-compatibility contract, see atlas_map_protocol.gd.
+## window_granularity_v2 (T-1152): the R5-redesigned string-tag granularity
+## ("Quarter"/"District"/"Region") — the only way to request the Region rung.
+## Omitted (empty string) by every caller that doesn't pass it.
 static func encode_atlas_layer_request(
 	body_id: String,
 	up_to: String = "Topography",
 	window_center: Variant = null,
 	window_n: int = 0,
 	window_granularity: int = 0,
-	window_min_wl_m: int = 0
+	window_min_wl_m: int = 0,
+	window_granularity_v2: String = ""
 ) -> PackedByteArray:
 	return _amp().encode_atlas_layer_request(
-		_mp(), body_id, up_to, window_center, window_n, window_granularity, window_min_wl_m
+		_mp(),
+		body_id,
+		up_to,
+		window_center,
+		window_n,
+		window_granularity,
+		window_min_wl_m,
+		window_granularity_v2
 	)