Schema Diff compares against a cached schema, so a diff after a DDL change reports no differences

## What

Schema Diff's "Current Schema" option reads a schema passed in as a prop rather than reading the database. A diff taken right after a DDL change reports no differences.

## Where

src/components/SchemaDiff.tsx:35-39

```tsx
schema: readonly DetailedObject[];
...
export function SchemaDiff({ schema, connection }: SchemaDiffProps) {
```

Lines 81 and 83 resolve "current" to that prop:

```ts
const sourceSchema = sourceId === "current" ? schema : snapshots.find((s) => s.id === sourceId)?.schema || [];
const targetSchema = targetId === "current" ? schema : snapshots.find((s) => s.id === targetId)?.schema || [];
```

Nothing re-reads the database for "current". The snapshot button at line 56 deep-copies the same prop, so a snapshot taken from a stale prop is stale too.

Note the contrast: `fetchRemoteSchema` at line 102 does go to the server for a remote connection. Only the local "current" side is served from memory.

## Observed

Take a snapshot, run a DDL change, open Schema Diff and compare the snapshot against Current Schema. It reports "No differences found". Reloading the page and repeating the comparison shows the difference.

## Why this matters

Schema Diff exists to answer "what changed", and the one case where the answer matters most, a change made moments ago, is the case it gets wrong. It also generates migration SQL from that comparison, so a migration generated right after a DDL change can be empty or wrong.

## Suggested direction

Refresh the schema before computing a diff that involves "current", or invalidate whatever cache feeds the prop when a DDL statement runs. A visible "last read at" stamp beside the Current Schema option would also make a stale read obvious rather than silent.

Start in src/components/SchemaDiff.tsx, especially the schema prop, snapshot handling around line 56, and current-schema resolution at lines 81-83. Compare this path with fetchRemoteSchema at line 102 and trace how the local schema prop changes after DDL execution. Done means a diff involving Current Schema reflects a recent database change and generated migration SQL is not empty or incorrect.

Written by the indexing model from the issue text.