feat: add collaborative interview scheduling

Add candidate decisions, co-interviewer accounts, scheduled interview inbox and calendar views, candidate-safe meeting links, shared documents, and private live notes backed by RabbitMQ.

Extend the disposable integration environment to validate PostgreSQL migrations, seeded users, interview lifecycle behavior, and RabbitMQ fanout.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/internal/eventbus/eventbus.go

@@ -0,0 +1,86 @@
+package eventbus
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"time"
+)
+
+type InterviewNoteEvent struct {
+	InterviewID  uint      `json:"interviewId"`
+	ID           uint      `json:"id"`
+	AuthorUserID uint      `json:"authorUserId"`
+	AuthorName   string    `json:"authorName"`
+	Body         string    `json:"body"`
+	CreatedAt    time.Time `json:"createdAt"`
+}
+
+type IEventBus interface {
+	PublishInterviewNote(context.Context, InterviewNoteEvent) error
+	SubscribeInterviewNotes(context.Context) (<-chan InterviewNoteEvent, error)
+	Close() error
+}
+
+var ErrClosed = errors.New("event bus is closed")
+
+type MemoryBus struct {
+	mu          sync.RWMutex
+	subscribers map[chan InterviewNoteEvent]struct{}
+	closed      bool
+}
+
+func NewMemoryBus() *MemoryBus {
+	return &MemoryBus{subscribers: make(map[chan InterviewNoteEvent]struct{})}
+}
+
+func (b *MemoryBus) PublishInterviewNote(ctx context.Context, event InterviewNoteEvent) error {
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	if b.closed {
+		return ErrClosed
+	}
+	for subscriber := range b.subscribers {
+		select {
+		case subscriber <- event:
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+	return nil
+}
+
+func (b *MemoryBus) SubscribeInterviewNotes(ctx context.Context) (<-chan InterviewNoteEvent, error) {
+	b.mu.Lock()
+	if b.closed {
+		b.mu.Unlock()
+		return nil, ErrClosed
+	}
+	ch := make(chan InterviewNoteEvent, 16)
+	b.subscribers[ch] = struct{}{}
+	b.mu.Unlock()
+	go func() {
+		<-ctx.Done()
+		b.mu.Lock()
+		if _, ok := b.subscribers[ch]; ok {
+			delete(b.subscribers, ch)
+			close(ch)
+		}
+		b.mu.Unlock()
+	}()
+	return ch, nil
+}
+
+func (b *MemoryBus) Close() error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.closed {
+		return nil
+	}
+	b.closed = true
+	for subscriber := range b.subscribers {
+		close(subscriber)
+	}
+	clear(b.subscribers)
+	return nil
+}