fix(backend): close SSE reconcile race that could permanently drop a user's event triggers

[LukasHirt]

Summary

The per-user SSE consumer manager (backend/pkg/sse/manager.go) had two related timing/race bugs that could cause event-triggered workflows to silently never fire uploads:

1. Dead consumer never retried. consumeForUser inserted its m.active[userID] entry before calling GetAutomation, but never removed it if GetAutomation failed (e.g. the user has an event trigger but hasn't connected automation yet, or their app-password was revoked). Since the entry never left m.active, every later reconcile() pass saw the user as "already active" and never retried the consumer, even after automation was later connected — the consumer was dead forever.

   Fix: consumeForUser now removes its own m.active entry when it exits due to a GetAutomation failure. All the other return paths happen because ctx was cancelled by reconcile's removal logic or by shutdown — those already remove the entry themselves, so consumeForUser must not also delete it there (that would race with a fresher entry a later reconcile pass may have already installed for the same userID). This is guarded with a small per-entry generation id (activeConsumer.id) so self-cleanup only ever deletes the entry it actually owns.

2. Up-to-30s blind window. reconcile() only ran on a fixed 30s ticker, so a workflow's event trigger being created/enabled, or a user's automation being connected, could miss an upload that happened before the next tick opened that user's SSE stream.

   Fix: added Manager.Kick() — a non-blocking, drop-if-pending signal — that Start's select loop also listens on alongside the ticker. Wired it into the two write paths that can affect the wanted-consumer set: WorkflowsHandler.syncTriggerIndex (workflow create/update, in pkg/service/workflows.go) and automation.Service.Connect (in pkg/automation/automation.go). Both take an optional Kick()-satisfying interface so they stay decoupled from the concrete *sse.Manager type; backend/pkg/command/server.go was reordered to construct the sse.Manager first and wire it into both.

Test plan

TDD: wrote the following tests against the old code first and watched them fail for the right reason, then implemented the fix and watched them pass.

• TestReconcileRetriesConsumerAfterTransientGetAutomationFailure (new, pkg/sse/manager_test.go) — reproduces bug chore(deps): Bump actions/setup-node from 6.3.0 to 7.0.0 #1: automation missing on first reconcile, connected later, asserts the consumer is retried.
• TestKickTriggersImmediateReconcile (new, pkg/sse/manager_test.go) — reproduces bug chore(deps): Bump actions/checkout from 6.0.2 to 7.0.0 #2: uses a "warm-up" trigger to prove Start's select loop is actually running (avoiding a scheduling race), then asserts Kick() picks up a newly-added trigger well within the (1-hour, in the test) ticker interval.
• All existing pkg/sse tests continue to pass, including TestReconcileStartsAndStopsConsumersAsTriggersChange (removal-path coverage).

Ran locally, matching CI's backend job exactly:

• go build ./...
• go vet ./...
• go test ./...
• go test ./... -race (extra, not in CI but run to validate the new mutex/generation-id logic)
• go build -tags=e2e ./... / go vet -tags=e2e ./... (constructor signature changes didn't break e2e compilation)

No unrelated code touched — the share-file action node commits on this branch's ancestry were left untouched; this PR only modifies pkg/sse/manager.go (+tests), pkg/service/workflows.go, pkg/automation/automation.go, and pkg/command/server.go wiring.