feat: Add Railway integration

[12458]

This PR implements the base Railway integration (#2910) using the new wizard-based setup flow.

What changed

Backend (pkg/integrations/railway/)

• GraphQL Client (client.go): Wrapped the Railway GraphQL API (v2 backboard), adding methods for Verify, ListWorkspaces, ListProjects, GetProjectDetails, TriggerDeploy (redeployment), GetDeployment (polling check), and rule management.
• Setup Wizard (setup_provider.go): Multi-step wizard allowing capability selection, Workspace Token input, validation, and secure secrets storage.
• Webhook Provisioning (webhook_handler.go): Dynamically loads project details to extract the correct workspace ID, and automatically creates the platform notification rule on Railway (notificationRuleCreate).
• On Deployment Trigger (on_deployment.go): Subscribes to and parses Railway platform notifications (including nested resource payloads) to emit status updates.
• Trigger Deploy Action (trigger_deploy.go): Triggers service redeployment and runs a polling loop checker. Emits to the success or failed channel depending on terminal states.
• Blank Import (pkg/registryimports/registryimports.go): Registered the railway integration package.

Frontend

• Branding Assets (railway.svg): Added the official Railway branding logo.
• Icon Registry (integrationIconMaps.ts): Mapped "railway" to the SVG logo.
• Canvas Mappers (web_src/src/pages/workflowv2/mappers/railway/): Added mappers (base.ts, on_deployment.ts, trigger_deploy.ts, index.ts) for custom styling, labels, configuration details, execution outcomes, and timelines.
• Mappers Registry (web_src/src/pages/workflowv2/mappers/index.ts): Integrated the mappers into the main workflow v2 canvas list.

Documentation (docs/components/Railway.mdx)

• Generated component documentation automatically via make gen.components.docs.

Why

To enable SuperPlane workflows to redeploy services and respond to deployment state changes on the Railway platform.

How

• The Graphql Backboard API is queried with Workspace API Tokens.
• Platform notification rule configurations (Deployment.* statuses) are mapped to standard unguessable UUID webhook paths.
• Execution polling hook executes every 15 seconds while state is active, and terminates on SUCCESS or failure/cancellation statuses (FAILED, CRASHED, REMOVED, SKIPPED, SLEEPING).

Verification

• Backend tests: Passed all 49 unit tests in pkg/integrations/railway.
• Gofmt / Lints / App build: Passed revive, go build cmd/server, and gofmt.
• Frontend checks: Passed eslint, check.build.ui (production compile), and prettier format check.

[superplanehq-integration]

👋 Commands for maintainers:

• /sp start - Start an ephemeral machine (takes ~30s)
• /sp stop - Stop a running machine (auto-executed on pr close)