fix(core): restore hreflang links in bundled SSR

[masonjames]

What does this PR do?

Keeps the configured locale list available when Vite loads EmDash through more than one SSR module chunk. This restores the hreflang links that were skipped when the UI and middleware read separate module instances, and adds a regression test that recreates that boundary.

Closes #2061

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main.
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion: Not applicable; this is a bug fix.

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: OpenAI Codex (GPT-5)

Screenshots / test output

• pnpm build
• pnpm typecheck
• pnpm lint
• pnpm --filter emdash exec vitest run tests/unit/i18n/config.test.ts (1 test passed)
• Full core run: 5,014 tests passed; the only failure is the pre-existing macOS /var vs /private/var path assertion in virtual-modules.test.ts.
• No admin UI strings or screenshots are involved.

[changeset-bot]

🦋 Changeset detected

Latest commit: 31ebda6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 17 packages

Name	Type
emdash	Patch
@emdash-cms/cloudflare	Patch
@emdash-cms/sandbox-workerd	Patch
@emdash-cms/plugin-mcp-smoke	Patch
@emdash-cms/fixture-perf-site	Patch
@emdash-cms/perf-demo-site	Patch
@emdash-cms/cache-demo-site	Patch
@emdash-cms/do-demo-site	Patch
@emdash-cms/do-solo-demo-site	Patch
@emdash-cms/admin	Patch
@emdash-cms/auth	Patch
@emdash-cms/blocks	Patch
@emdash-cms/gutenberg-to-portable-text	Patch
@emdash-cms/x402	Patch
create-emdash	Patch
@emdash-cms/auth-atproto	Patch
@emdash-cms/plugin-embeds	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

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commit: 31ebda6

[emdashbot]

This is the right fix for the problem described in #2061. Moving the i18n config from a module-scoped variable to a Symbol.for("emdash:i18n-config") slot on globalThis matches the repository's established singleton pattern (used in request-context.ts, settings/index.ts, and the middleware runtime/setup holders) and directly addresses Vite/Rollup duplicating modules across SSR chunks. The regression test recreates that boundary by using vi.resetModules() and dynamic re-imports, and it would fail under the old module-level _config implementation.

I checked:

• The new packages/core/src/i18n/config.ts singleton store and all updated consumers (getI18nConfig, isI18nEnabled, resolveConfiguredLocale, getFallbackChain).
• Callers of setI18nConfig/getI18nConfig, including the middleware virtual-config initialization and seo/hreflang.ts.
• The new unit test in packages/core/tests/unit/i18n/config.test.ts.
• The changeset (correct package emdash, user-facing wording).

No blocking issues, convention violations, or new logged-out queries. LGTM.