fix(elk): use balanced Brandes-Koepf placement in the default preset

.changeset/bright-elk-centering.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+Use balanced Brandes-Koepf placement for the default ELK preset to improve alignment of branches and composite-state entries. Preserve named non-default presets and explicit placement/alignment options, including `NONE`. Some diagrams may become wider or taller; `depthFirst` retains the previous default layout.

.changeset/elk-layout-presets.md

@@ -6,10 +6,10 @@ feat: `elk.preset` picks a named combination of the options that decide where no
 
 Three options settle node positions, and they sit in different phases of the layout: which layer a node lands in, where it goes within that layer, and which edges get reversed to make the graph acyclic. Choosing them well means knowing all three interact; `preset` names the combinations worth using.
 
-- `default` — network simplex layering and placement with depth-first cycle breaking at the top level; subgraph contents are placed with Brandes-Koepf. Depth-first breaking gives shorter back edges on graphs that loop.
+- `default` — network simplex layering, balanced Brandes-Koepf placement at the top level and inside subgraphs, and depth-first cycle breaking. Balanced placement centres branches and composite-state entries; depth-first breaking gives shorter back edges on graphs that loop.
 - `legacy` — reproduces what earlier versions actually rendered: Brandes-Koepf placement with ELK's own greedy cycle breaking.
-- `modelOrder` — as `default`, but breaks cycles by greedy model order, which disturbs declaration order least at the cost of longer back edges.
-- `depthFirst` — a name for what `default` already is, so a diagram can say depth-first rather than rely on the default staying put.
+- `modelOrder` — as `depthFirst`, but breaks cycles by greedy model order, which disturbs declaration order least at the cost of longer back edges.
+- `depthFirst` — the previous default: network simplex layering and top-level placement, Brandes-Koepf placement inside subgraphs, `NONE` alignment, and depth-first cycle breaking.
 
 ```yaml
 ---
@@ -20,10 +20,10 @@ config:
 ---
 ```
 
-Setting `layeringStrategy`, `nodePlacementStrategy` or `cycleBreakingStrategy` explicitly overrides the preset for that one option and leaves the rest in place, so a preset is a starting point rather than a lock.
+Setting `layeringStrategy`, `nodePlacementStrategy`, `nodePlacementAlignment` or `cycleBreakingStrategy` explicitly overrides the preset for that one option and leaves the rest in place, so a preset is a starting point rather than a lock.
 
-**Node placement changes from `BRANDES_KOEPF` to `NETWORK_SIMPLEX`, so existing ELK diagrams will lay out differently.** `preset: legacy` restores the previous behaviour, and is the single switch for it — this is the net change against the last release, measured from what shipped rather than from any intermediate state.
+**Node placement keeps `BRANDES_KOEPF`, but its alignment changes from `NONE` to `BALANCED` and cycle breaking from `GREEDY` to `DEPTH_FIRST`, so existing ELK diagrams will lay out differently.** `preset: legacy` restores the previous behaviour, and is the single switch for it — this is the net change against the last release, measured from what shipped rather than from any intermediate state.
 
-Subgraph contents keep `BRANDES_KOEPF`, which is deliberately not the root's strategy: network simplex inside a frame produced routes that left the subgraph on its bounding-box corner. The two sides are tuned independently, so `nodePlacementStrategy` set explicitly still applies to both.
+Subgraph contents use `BRANDES_KOEPF` under every preset. For `modelOrder` and `depthFirst` that is deliberately not the root's strategy: network simplex inside a frame produced routes that left the subgraph on its bounding-box corner. The two sides are tuned independently, so `nodePlacementStrategy` set explicitly still applies to both.
 
 Note that `legacy` uses `GREEDY` cycle breaking rather than the `GREEDY_MODEL_ORDER` the schema previously advertised. That default was declared in the schema but never listed in the shipped defaults, so it reached ELK as undefined and ELK's own default applied — `legacy` reproduces what was rendered, not what was documented.

docs/config/setup/defaultConfig/variables/configKeys.md

@@ -12,4 +12,4 @@
 
 > `const` **configKeys**: `Set`<`string`>
 
-Defined in: [packages/mermaid/src/defaultConfig.ts:357](https://github.com/mermaid-js/mermaid/blob/master/packages/mermaid/src/defaultConfig.ts#L357)
+Defined in: [packages/mermaid/src/defaultConfig.ts:356](https://github.com/mermaid-js/mermaid/blob/master/packages/mermaid/src/defaultConfig.ts#L356)