v0.2.0 (1/N): public API surface — interfaces + BridgeOp enum

Establishes the contract layer the rest of v0.2.0 builds on. Pre-1.0
SemVer break: ModelPublisher::publishEntityChange() now takes BridgeOp
instead of a raw string.

Interfaces (Symfony idiom: same namespace as concrete, like HubInterface
next to Hub):
  - PublisherInterface — publish(string, array, bool)
  - ModelPublisherInterface — publishEntityChange(object, BridgeOp)
  - CorrelationContextInterface — set/get/clear

App code should typehint these instead of the concretes so swappable
implementations (offline-buffer publisher, multi-hub fan-out, request-
stamp correlation) remain non-breaking. Concrete classes implement them
unchanged; autowire continues to inject the implementations transparently.

BridgeOp: PHP 8.1 string-backed enum with cases Upsert / Delete /
Replace / Event matching PLAN.md §4's envelope `op` wire format.
Internal call sites updated; tests use the cases directly.

Switched typehints:
  - ModelPublisher ctor: PublisherInterface + CorrelationContextInterface
  - DoctrineBridgeListener ctor: ModelPublisherInterface
  - HealthController ctor: PublisherInterface (still emits `Publisher`
    as bundle canary value — `::class` resolves to the concrete class
    name regardless of typehint, so bundled-supervisor.sh's grep stays
    green)
  - skeleton PingController ctor: PublisherInterface (canonical app
    pattern — example/todo has no Publisher consumer to update)

Drive-by: removed deprecated setAccessible(true) call in
ModelPublisher::extractId — PHP 8.1+ allows reflection without it.

PHPStan + cs-fixer + PHPUnit (17/17) + maker snapshot all pass; dev
container compiles in the example app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

framework/php/src/Publisher.php

@@ -8,22 +8,22 @@ use Symfony\Component\Mercure\HubInterface;
 use Symfony\Component\Mercure\Update;
 
 /**
- * Publishes envelopes onto the bridge's Mercure hub.
+ * Default implementation of {@see PublisherInterface}: a thin wrapper over
+ * `symfony/mercure`'s `HubInterface` that JSON-encodes the envelope and
+ * forwards the publish.
  *
  * Topic conventions and envelope shape are defined in PLAN.md §4.
- * Reactive-model-aware helpers (publishModelUpdate, etc.) arrive with
- * the model layer in Phase 2.
+ * Application code should typehint `PublisherInterface` instead of this
+ * concrete class so swappable implementations (offline buffer, multi-hub
+ * fan-out) remain a non-breaking change.
  */
-final readonly class Publisher
+final readonly class Publisher implements PublisherInterface
 {
     public function __construct(
         private HubInterface $hub,
     ) {
     }
 
-    /**
-     * @param array<string, mixed> $envelope
-     */
     public function publish(string $topic, array $envelope, bool $private = false): string
     {
         return $this->hub->publish(new Update(