Fix chevron over-count, plane-lock diagonal frame connectivity, true one-way travel, iris shield independence

Chevron placement: the "protruding elbow" heuristic marked every
convex corner of a smooth ring as a chevron, which for a true
octagon/circle is *every* corner - producing 8 chevrons instead of a
deliberate subset. Replaced with a fixed, configurable count
(gate.chevron-count, default 7) evenly spaced along the ring's actual
geometric walk order.

Frame flood-fill leaking into unrelated structures: the diagonal
("stepped ring") connectivity fix from two commits ago used a full 3D
26-neighbor search, which let the flood leak sideways through the
ring's thickness into any other nearby structure sharing a frame
material (e.g. gilded blackstone used decoratively on a backdrop
wall), putting chevrons on it. The scan now bootstraps with a small
orthogonal-only flood to find the ring's plane first, then only
allows diagonal connectivity within that plane - never through depth.

One-way travel, properly this time: RuntimeGate gained an `outgoing`
flag, set true only on the gate that was actually dialed. The
teleport listener now only matches outgoing gates, so the destination
shows the event horizon but isn't walkable - stepping into it does
nothing, and only the dialing side can send a player anywhere.

Iris shield: it's a physical barrier independent of the wormhole, not
tied to "connected" state. Closed always means iris-shield-material
(default changed from IRON_BLOCK to BEDROCK per feedback), whether or
not the gate is even dialed right now. Only when the shield is open
does the idle/connected distinction (air vs event horizon) apply.
applyIrisMaterial() centralizes this so link, restart re-scan,
open/close, and the shield toggle all agree.

stargate-paper/src/main/resources/config.yml

@@ -31,7 +31,10 @@ gate:
   # Mix and match to match your build (the default matches an obsidian/gilded-blackstone
   # ring). The ring can be any size or shape, as long as it's a single connected loop
   # made only of these materials with a fully sealed hollow interior - no fixed template
-  # or size is required.
+  # or size is required. "Connected" includes diagonal stepping (round rings need that
+  # at their corners), but only within the ring's own flat plane - a nearby structure
+  # built from the same materials won't get pulled in just because it touches the ring
+  # through its thickness.
   frame-materials:
     - OBSIDIAN
     - GOLD_BLOCK
@@ -39,19 +42,22 @@ gate:
     - BIRCH_PLANKS
     - OAK_PLANKS
   # Chevrons aren't a separate material you place. The plugin flood-fills the ring,
-  # walks it in geometric order, and picks out the blocks that stick further outward
-  # than their ring-neighbours - the "elbow" points of the shape, same as a real
-  # Stargate's chevron placement - then swaps just those to chevron-lit-material while
-  # dialing/open, restoring whatever they looked like at rest when the gate closes.
+  # walks it in geometric order, and picks this many blocks, evenly spaced around the
+  # ring's actual perimeter (not raw scan order) - then swaps just those to
+  # chevron-lit-material while dialing/open, restoring whatever they looked like at
+  # rest when the gate closes.
   chevron-lit-material: GLOWSTONE
-  # The interior has three looks, matching SG-1: idle (not connected) is just empty
-  # air - you can see straight through the ring. Connected, it's the event horizon
-  # (iris-open-material) UNLESS the iris shield is closed, in which case it shows
-  # iris-shield-material instead and blocks all travel even though the gate is active.
-  # The shield is toggled with a button placed directly below the control sign.
+  chevron-count: 7
+  # The interior's look is driven by two independent things, matching SG-1:
+  #   - The iris shield: a physical barrier toggled with a button placed directly below
+  #     the control sign. Closed means closed - iris-shield-material, solid, blocking
+  #     everything - REGARDLESS of whether a wormhole is even active right now.
+  #   - Whether the shield is open: then it's iris-open-material (the event horizon)
+  #     if the gate is actively connected, or iris-idle-material (just empty air, you
+  #     see straight through) if it's just sitting there dialed to nothing.
   iris-idle-material: AIR
   iris-open-material: WATER
-  iris-shield-material: IRON_BLOCK
+  iris-shield-material: BEDROCK
   max-frame-blocks: 300
   max-iris-blocks: 200
   min-frame-blocks: 8