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

[roncodes]

What

• New Socket helper exposed as fleetbase.socket; fleetbase.socket.token(options?) calls POST socket/token and resolves to { token, expires_in, expires_at } (exported type SocketTokenResponse).
• setAdapter() also moves the socket helper to the new adapter.
• README: new Realtime socket tokens section showing the server-side mint with a secret key, then the browser connecting with socketcluster-client using an in-memory authEngine / socket.authenticate(token) and refreshing ~60 s before expiry.
• Changeset (minor). No version bump.

Why

Fleetbase realtime channels are moving to authenticated subscriptions. API customers need a supported way to exchange their secret key for a short-lived socket token on their own server, so the browser only ever sees the token.

Test plan

• Unit tests in tests/core.test.ts cover the request path/body/options, adapter replacement and error propagation (100% coverage gate).
• 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 #45, feat(socket-auth): add customer.socketToken() for realtime channels storefront-js#22, feat(socket-auth): add socket->token() to mint realtime socket tokens fleetbase-php#28 — SDK socket token helpers
• fleetbase/fleetbase.io#120 — docs and migration guide

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a502a95) to head (aaa39eb).

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v2.1.0       #45   +/-   ##
================================================
  Coverage          100.00%   100.00%           
================================================
  Files                  17        18    +1     
  Lines                 855       860    +5     
  Branches              143       143           
================================================
+ Hits                  855       860    +5     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.