refactor(view): drop mutual conflict; align with multi-driver pattern

[markshust]

Summary

PR #88 added Composer `conflict` declarations between `marko/view-latte` and `marko/view-twig`. This drops them, aligning view with the same pattern used by `marko/database`, `marko/cache`, `marko/queue`, etc. — where both drivers can be installed simultaneously and Marko's DI catches the double-binding at boot via `BindingConflictException`.

Why drop the conflicts?

Three reasons:

1. Marko already has the canonical detection mechanism. `BindingConflictException` throws at boot time when two modules bind the same interface. That's the framework's loud, expressive error path. Composer `conflict` declarations duplicate this in a less expressive medium — Composer can only say "incompatible," not "two modules bind ViewInterface, remove one."

2. O(n²) maintenance burden. Each new driver in a family requires updating every existing sibling's `conflict` block. PR #91 was going to ship a CI test enforcing sync between `known-drivers.php` and these conflict blocks — but that's infrastructure to maintain other infrastructure. `known-drivers.php` alone is enough source of truth.

3. Monorepo asymmetry. Because of the conflicts, view-twig couldn't sit in `require` next to view-latte — it had to live as a "phantom" via root `autoload-dev` namespace mappings, while view-latte was fully installed. After this change, view-twig is a regular monorepo package, fully symmetric with view-latte. Matches how database-mysql + database-pgsql coexist today.

What changed

• Removed `"conflict": {"marko/view-twig": "*"}` from `packages/view-latte/composer.json`
• Removed `"conflict": {"marko/view-latte": "*"}` from `packages/view-twig/composer.json`
• Deleted `packages/view-latte/tests/ComposerConflictTest.php` (asserted the conflict declaration that no longer exists)
• Removed the conflict assertion test in `packages/view-twig/tests/PackageTest.php`
• Added `marko/view-twig` to root `composer.json`'s `repositories[]` and `require` (mirrors view-latte)
• Removed the phantom `Marko\View\Twig\: packages/view-twig/src/` mapping from root `autoload-dev` (no longer needed — view-twig's own composer.json autoload kicks in via path repo install)
• Removed `twig/twig` from root `require-dev` (now transitive via view-twig's `require`)
• Updated `packages/framework/tests/RootComposerJsonTest.php` — added view-twig to the `$allPackages` array, bumped the "70 packages" descriptions to 71

Trade-off

Failure detection moves from `composer install` time to boot time. In practice the gap is seconds (any subsequent request triggers boot), and the boot-time error message is more actionable than Composer's dependency-resolution failures. Aligned with Magento's long-established prior art (module conflicts caught at DI level, not at composer.json) — which Marko inherits its DI heritage from.

Downstream impact

This blocks/feeds two open plans:

• PR feat: centralize driver registries with known-drivers.php pattern #91 (known-drivers-registry) — its tasks 008–024 each had an "add mutual conflict blocks" sub-step. Those sub-steps will be dropped in a follow-up commit to that PR. The `KnownDriversValidator` helper loses its `assertConflictBlocksMatch()` method.
• admin-panel-engine-siblings (separate plan) — also dropping the planned conflict between `admin-panel-latte` and `admin-panel-twig` (which was modeled on PR feat: add Twig template engine driver as sibling to Latte #88's pattern).

Test plan

• `packages/view/tests/` — 43 tests pass
• `packages/view-latte/tests/` — 42 tests pass
• `packages/view-twig/tests/` — 52 tests pass
• `packages/framework/tests/` — 27 tests pass (RootComposerJsonTest updated for the new package count)
• `composer update` resolves with both view-latte and view-twig installed simultaneously

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