fix(dashboard): use active node registry authority (#2145)

## Summary

- reuse the dashboard server's initialized `centralCore` for all
node-management routes
- preserve the legacy fallback only when no shared central authority is
provided
- never close the server-owned central authority from an individual
request
- cover node list and registration with regression tests that fail if a
route constructs its own `CentralCore`

## Problem

With the dashboard running on the PostgreSQL backend, `/api/nodes` and
`POST /api/nodes` bypassed the server's initialized PostgreSQL-backed
`centralCore` and constructed a separate legacy `CentralCore()`. Reads
could hit the wrong registry, while writes failed with a null SQLite
handle (`Cannot read properties of null (reading 'prepare')`). The same
pattern affected node detail, health, path-mapping, version,
plugin-sync, and Docker-config endpoints.

## Verification

- targeted regression: 2 tests passed
- dashboard typecheck passed
- ESLint passed for changed TypeScript files
- strict changeset validation passed
- dashboard production build passed
- `pnpm test:gate` passed against an isolated PostgreSQL 16 cluster:
  - engine core: 294 tests
  - PostgreSQL gate: 122 tests
  - CLI CI-shape: 63 tests

## Changeset

Patch release for `@runfusion/fusion`.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Improved multi-node management by keeping node operations connected to
the active PostgreSQL registry.
* Updated node listing, registration, configuration, health, version,
plugin, path, and Docker configuration routes for more consistent
behavior.
* Preserved Docker configuration validation and safe response handling.

* **Tests**
* Added coverage for retrieving and registering nodes through the active
registry.
* Verified successful node creation responses and handling of optional
configuration fields.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.changeset/postgres-node-registry-routes.md

@@ -0,0 +1,7 @@
+---
+"@runfusion/fusion": patch
+---
+
+summary: Keep multi-node management connected to the active PostgreSQL registry.
+category: fix
+dev: Node CRUD, health, path, version, plugin, and Docker-config routes now reuse the server-injected CentralCore.