feat: add Twig template engine driver as sibling to Latte

[markshust]

Summary

• Adds new marko/view-twig driver package — full Twig 3 engine with strict_variables (loud errors), HTML autoescape, and module-namespaced template resolution
• Refactors marko/view to be genuinely driver-neutral — removed Latte-biased extension and strict_types defaults; dropped ViewConfig::strictTypes() accessor
• Refactors marko/view-latte to ship its own config and new LatteViewConfig class (architectural symmetry with TwigViewConfig)

Architectural changes

Interface/driver split tightened. Before this PR, marko/view shipped .latte as its default view.extension and a Latte-specific strict_types flag — biasing the interface package toward one driver. Now each driver ships its own config/view.php with its own defaults; marko/view only owns the truly shared keys (cache_directory, auto_refresh).

Mutual exclusion at install time. Both drivers declare "conflict": {"other-driver": "*"} in composer.json. Installing both fails loudly at composer install rather than at runtime via BindingConflictException.

Driver-specific config accessors live with their drivers. New TwigViewConfig (in view-twig) and LatteViewConfig (in view-latte) host their respective driver-only settings. No driver-specific accessors pollute the shared ViewConfig.

No silent fallbacks. Every value TwigViewConfig and LatteViewConfig expose goes through ConfigRepositoryInterface — missing keys throw ConfigNotFoundException. All defaults live in config files, never in code.

Twig defaults (config/view.php)

• extension: '.twig'
• strict_variables: true — undefined variables throw, matching Marko's loud-errors principle
• autoescape: 'html' — safe default for web apps
• debug: false
• charset: 'UTF-8'

Users override any of these in their app-level config/view.php.

Cross-cutting updates

• NoDriverException now lists both marko/view-latte and marko/view-twig with composer require commands
• Skeleton lists both drivers in its suggest block (Twig first for broader ecosystem familiarity); skeleton stays engine-agnostic with no hard view-driver dep
• Docs site registers twig as a Shiki language for syntax highlighting (built-in, no custom grammar needed)
• New docs page at docs/src/content/docs/packages/view-twig.md mirrors the existing view-latte.md structure
• marko/view and marko/view-latte docs updated to reflect the driver-neutral interface package and the new LatteViewConfig class

Out of scope (follow-up plan)

• marko/admin-panel ships only .latte templates — users installing view-twig instead of view-latte would hit template-not-found errors. The next plan extracts admin-panel templates into engine-specific sibling packages (marko/admin-panel-latte, marko/admin-panel-twig) and adds a CrossEngineTemplateParityTest in marko/view's test suite to mechanically enforce parity for all core engines.

Test plan

• All marko/view tests pass (43 tests)
• All marko/view-latte tests pass (28 tests — refactored LatteEngineFactory mocks updated)
• All marko/view-twig tests pass (46 tests covering config, engine factory, module loader, view, module bindings, package structure)
• All marko/skeleton tests pass (16 tests including new suggest-block assertions)
• Docs site builds with no warnings about unknown twig language
• Composer validates view-twig and refactored view-latte composer.json files
• Standards enforced across all changed PHP files (strict_types, readonly classes, typed constants, @throws tags, expectation chaining)

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