Load GraphQL schema from file for autocomplete

[VDShelk]

Summary

Adds a "Load Schema from File…" item to the existing GraphQL schema dropdown that lets users populate the editor's autocomplete schema from a local file instead of (or in addition to) running an introspection request against a server.

Useful when:

• Working against a private/staging API where introspection is disabled or unreachable
• Working offline against a locally-generated SDL or saved introspection result
• Iterating on a schema before the server is even up

Submission

• This PR is a bug fix or small-scope improvement.
• If this PR is not a bug fix or small-scope improvement, I linked an approved feedback item below.
• I have read and followed CONTRIBUTING.md.
• I tested this change locally.
• I added or updated tests when reasonable.

Scope (re. CONTRIBUTING.md)

I believe this fits the "small-scope improvement directly tied to existing behavior" bucket — happy to file an approved feedback item instead if you'd prefer:

• No new tauri commands, no new database tables, no new model types.
• Reuses the existing graphql_introspection table and models_upsert_graphql_introspection command.
• Reuses the existing dropdown, the existing buildClientSchema parser, the existing error UI, and the existing autoIntrospectDisabled localStorage toggle.
• Frontend-only: 2 files, ~125 net insertions.

What it accepts

The file picker accepts .graphql / .graphqls / .gql / .json. The parser normalizes three shapes into the single { data: <introspection> } JSON that the hook already persists:

1. Introspection result with data wrapper — what getIntrospectionQuery() returns from a server: { "data": { "__schema": ... } }. Stored verbatim.
2. Introspection result without wrapper — { "__schema": ... }. Wrapped before storage.
3. SDL — fed through buildSchema() → introspectionFromSchema() from graphql-js (already a direct dep), then wrapped before storage.

If parsing fails, the existing "Introspection Failed" error UI is reused.

Auto-disable behavior

After a successful file load, Automatic Introspection is toggled off for that specific request. Without this, the next URL/method edit re-fires the introspection effect and clobbers the schema the user just loaded from disk. The user can re-enable from the same dropdown — the existing per-request toggle is unchanged.

This is the only opinionated UX choice in the PR; happy to revert if you'd rather not touch the toggle and let the user manage it manually.

Test plan

• tsc --noEmit clean
• vp lint clean (no new warnings)
• vp fmt --check clean
• Manual: load SDL .graphql file → autocomplete + Documentation panel work
• Manual: load introspection .json with { "data": { "__schema": … } } → same
• Manual: load bare { "__schema": … } .json → same
• Manual: load a non-GraphQL file → red error state with useful parser message
• Manual: after upload, edit URL → schema is preserved (auto-introspect off)
• Manual: re-enable Automatic Introspection → next URL edit overwrites the upload (expected)
• Manual: Clear → wipes the stored schema

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