Add symfony-specialist

[thomas-cautres]

feat: add symfony-specialist subagent

Summary

• Adds a new symfony-specialist subagent for Symfony 6.x / 7.x / 8.0 and Doctrine ORM development
• Updates all required files per CONTRIBUTING.md (main README, category README, plugin.json, marketplace.json)
• Bumps voltagent-lang plugin version from 1.0.2 to 1.0.3

What the agent does

The symfony-specialist is a version-aware PHP framework expert that reads composer.lock to detect the Symfony and Doctrine versions in use, then adapts all recommendations accordingly:

• Symfony 6.4 (LTS) — Webpack Encore, classic security config, PHP 8.1+
• Symfony 7.x — AssetMapper, #[MapRequestPayload] / #[MapQueryParameter], Clock component, PHP 8.2+
• Symfony 8.0 — PHP 8.4 required, symfony/object-mapper for DTO transformations, constructor extractor enabled by default, amphp/http-client 5.3.2+

Coverage

Area	Details
Doctrine ORM	Entity design, associations, inheritance mapping, embeddables, DQL, query builder, lifecycle callbacks, DBAL, migrations, second-level cache
API	API Platform, DTO with ObjectMapper (Symfony 8), Lexik JWT, OAuth2, OpenAPI
Async	Messenger stamps (DelayStamp, HandledStamp, DispatchAfterCurrentBusStamp), middleware, retry strategy with jitter, failure transport
Security	Security Voters, #[IsGranted], password hashers, CSRF, firewalls, scheb/2fa-bundle, NelmioSecurityBundle, composer audit
Testing	WebTestCase, PHPUnit, DAMADoctrineTestBundle, ApiTestCase, Panther
Deployment	Symfony CLI, FrankenPHP, dunglas/symfony-docker, Deployer, Platform.sh
Production	Blackfire.io, Monolog, Sentry, liip/monitor-bundle, OpenTelemetry
Modern DX	AssetMapper / Importmap, Stimulus / Turbo, PHP 8 attributes, AutowireAttribute, TaggedIterator

Documentation source

All Symfony 8.0-specific features (ObjectMapper, PHP 8.4 requirement, amphp/http-client version) were verified against the official Symfony documentation (branch 8.0).