Phase 1 sub-commit 2: Symfony bundle internals

Bundle code for php-qml/bridge: BridgeBundle (AbstractBundle, autoloads
config/services.yaml), Publisher (thin wrapper over Mercure HubInterface
that enforces envelope-as-JSON), SessionAuthenticator (bearer-token
custom Symfony authenticator with problem+json failures), and
HealthController (GET /healthz readiness probe).

Composer constraints bumped to Symfony ^8.0 across the board (per user
request); mercure component to ^0.7. PHPUnit 11 suite covers Publisher
publish + private flag and SessionAuthenticator support/auth/failure
paths — 8 tests, 22 assertions, all green.

PLAN.md §13 updated to record the Symfony 8 minimum.

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

framework/php/config/services.yaml

@@ -0,0 +1,13 @@
+services:
+    _defaults:
+        autowire: true
+        autoconfigure: true
+
+    PhpQml\Bridge\:
+        resource: '../src/'
+        exclude:
+            - '../src/BridgeBundle.php'
+
+    PhpQml\Bridge\SessionAuthenticator:
+        arguments:
+            $expectedToken: '%env(default::BRIDGE_TOKEN)%'