bug: SSE event stream drops all events for worktree sessions (still present on current dev)

Re-opening the still-relevant bug from #35917, which was auto-closed after 60 days of inactivity.

Verified today on current dev (@5f9d9187c): packages/opencode/src/server/routes/instance/httpapi/handlers/event.ts:37 still gates the SSE stream on

event.location?.directory === instance.directory &&
  (event.location.workspaceID === undefined || event.location.workspaceID === workspaceID)

Worktree sessions emit events whose location.directory differs from the main instance directory, so the directory equality check filters out every worktree event — SSE subscribers see no activity for worktree sessions at all. Original repro details are in #35917.

The prior fix PR #35913 was closed by the automated PR cleanup (>1 month old, few reviews) — not rejected on merit. A rebased version of the same two-line fix is incoming.

Start in packages/opencode/src/server/routes/instance/httpapi/handlers/event.ts at line 37 and review how the SSE stream filters event locations for worktree sessions. Use the reproduction details in issue #35917 as context, then verify that worktree subscribers receive activity events and that the directory filtering behavior is covered before considering the issue done.