fix: remove context reaper to prevent background tabs from going stale

Background windows stopped updating because the reaper suspended contexts
after ContextSuspendAfter and fully reaped them after ContextTTL. Suspended
contexts had to re-run the page init function from scratch on reconnect,
losing the live-updating experience.

Contexts now live until the browser tab closes (beforeunload beacon) or
the server shuts down. The context map grows indefinitely — no background
reaper.

Removes: startReaper, reapOrphanedContexts, suspend/resume logic,
ContextSuspendAfter/ContextTTL config fields, lastSeenAt/suspended
context fields, and all associated tests.

context.go

@@ -42,8 +42,6 @@ type Context struct {
 	createdAt           time.Time
 	sseConnected        atomic.Bool
 	sseDisconnectedAt   atomic.Pointer[time.Time]
-	lastSeenAt          atomic.Pointer[time.Time]
-	suspended           atomic.Bool
 }
 
 // View defines the UI rendered by this context.
@@ -444,13 +442,6 @@ func (c *Context) resetPageState() {
 	c.mu.Unlock()
 }
 
-// suspend frees page-scoped resources while keeping the context shell alive
-// in the registry for seamless re-init on reconnect.
-func (c *Context) suspend() {
-	c.resetPageState()
-	c.suspended.Store(true)
-}
-
 // Navigate performs an SPA navigation to the given path. It resets page state,
 // runs the target page's init function (with middleware), and pushes the new
 // view over the existing SSE connection with a view transition animation.