feat(socket-auth): add socket->token() to mint realtime socket tokens

[roncodes]

What

• New Fleetbase\Sdk\Services\SocketService, exposed as $fleetbase->socket / $fleetbase->socket() / service('socket').
• $fleetbase->socket->token(array $options = []) sends POST socket/token and returns the decoded { token, expires_in, expires_at }. A server without realtime auth configured answers 404, raised as NotFoundException.
• The service is hand-written: the route is not yet in the locked Postman contract, so it is outside the generated endpoint services and docs/api-coverage.md. When the Postman collection gains the route it can move into the generated set.
• README section on server-side minting and the browser socket.authenticate(token) flow; CHANGELOG [Unreleased] entry. No version bump.

Why

Realtime channels are moving to authenticated subscriptions. PHP backends need a supported way to exchange their secret key for a short-lived token so that browsers never hold the API key.

Test plan

• tests/Fleetbase/SocketTest.php: request method/path and decoded payload; 404 maps to NotFoundException.
• FleetbaseTest service list includes socket.
• Verified by CI (not run locally).

Related PRs

Part of the authenticated realtime channels rollout (socket auth), one PR per repo:

• feat(socket-auth): authenticated realtime channels (tokens, authorizer, signed publish) core-api#290 — tokens, channel authorizer, signed HTTP publish (merge and tag first: fleetops and storefront require fleetbase/core-api ^1.6.69)
• feat(socket-auth): fleetops channel resolvers, driver socket tokens, per-customer tracking channel fleetops#358 — fleetops channel resolvers, driver socket tokens, per-customer tracking channel
• feat(socket-auth): storefront customer and checkout socket tokens, channel resolvers storefront#113 — customer and checkout socket tokens, storefront/checkout resolvers
• feat(socket-auth): Fleetbase socket server with JWT auth and signed internal publish fleetbase#704 — fleetbase/fleetbase-socket server, compose/helm/installer, console socket test page
• feat(socket-auth): authenticate the realtime socket with session socket tokens ember-core#97 — console socket service authenticates with session tokens
• feat(socket-auth): show channel authorization failures in the sockets viewer dev-engine#51 — sockets viewer shows authorization failures
• feat(socket-auth): authenticate realtime socket with driver socket tokens navigator-app#112 — driver app socket tokens
• feat(socket-auth): authenticate realtime socket with customer and checkout socket tokens storefront-app#65 — customer and checkout socket tokens
• feat(socket-auth): generate the socket auth key on install fleetbase-cli#11 — installer generates the socket auth key
• feat(socket-auth): add socket.token() to mint realtime socket tokens fleetbase-js#45, feat(socket-auth): add customer.socketToken() for realtime channels storefront-js#22, feat(socket-auth): add socket->token() to mint realtime socket tokens #28 — SDK socket token helpers
• docs(socket-auth): authenticated realtime channels and migration guide fleetbase.io#120 — docs and migration guide