Remove json-bigint from the frontend #153

Why

The backend now guarantees that no integer above Number.MAX_SAFE_INTEGER reaches the client:

• backend/graph_normalizer/utils.py:to_json_safe walks the entire /api/v1/graph-data payload and converts any int with abs(value) > 2**53 - 1 to a string.
• backend/snapshot_map/snapshot_mapping.py already emits snapshot_id as str.
• GET /api/v1/tables returns only strings.

So json-bigint on the frontend is dead weight: every response can be parsed with the native JSON.

Scope

Remove json-bigint and @types/json-bigint from frontend/package.json and replace every use with native JSON.parse / JSON.stringify:

• frontend/src/shared/lib/api.ts - jsonWithBigIntsAsStrings for both request stringify and response parse.
• frontend/src/pages/TableLayout.jsx - graph-data response parse, IndexedDB cache parse, error-body parse.
• frontend/src/pages/HomePage.jsx - tableHistory localStorage parse.
• frontend/src/pages/MetadataPage.jsx - parseJsonMaybe for table properties whose value is a JSON string.

Notes

• MetadataPage's parseJsonMaybe is the one case the backend guard does not cover: it parses arbitrary Iceberg table-property values that are themselves JSON strings, user for it the function in the backend of to_json_safe
• Do not touch frontend/src/shared/lib/searchParams.ts. It deliberately avoids JSON-parsing URL params so snapshot IDs stay strings; that is unrelated to json-bigint and must stay as is.
• Snapshot IDs must continue to be treated as strings throughout the UI - this issue removes the big-int parser, not the string-typed IDs.

Done when

• No json-bigint import remains under frontend/src, and neither package appears in frontend/package.json / package-lock.json.
• npm run lint, npm run format, npm run typecheck pass.
• A table with snapshot IDs above 2^53 renders correctly: Home history, snapshot selection, Timeline, Metadata, Graph, and the IndexedDB cache path (reload a previously loaded table).