fix(richtext-lexical): preserve logical text alignment

[ertugakmann]

What?

Preserve Lexical's logical text alignment values when converting to HTML.

Before: <p style="text-align: left;">Hello</p>

After: <p style="text-align: start;">Hello</p>

Explicit left alignment is also now preserved instead of being omitted.

Why?

start and end are logical CSS alignment values and should not be converted to physical left and right values. Converting them can cause incorrect alignment for RTL content.

How?

The Lexical → HTML converter now preserves the explicit alignment value instead of resolving start/end to physical values.

Added regression tests covering start, end, explicit left/right, and RTL direction.

Tests:

• pnpm vitest run packages/richtext-lexical/src/features/converters/lexicalToHtml/sync/alignment.spec.ts
• 5/5 passing

Fixes #17784

[ertugakmann]

The PR's alignment regression tests pass (5/5).

The CI failures appear unrelated to this change. The failing jobs are integration tests in unrelated areas:

• MongoDB: collections-graphql — payload is undefined during teardown.
• MongoDB: locked-documents — MongoServerError: Unable to write to collection 'payload._pages_versions' due to catalog changes.
• PostgreSQL read replica: postgres-vector — expected 2 results but received 0.

The only production change in this PR is the Lexical HTML alignment conversion in findConverterForNode.ts, with a focused regression test covering the reported behavior.

No changes were made to the unrelated failing tests or CI configuration.