fix(dynamodb): show items as plain JSON and stop double-encoding keys

[vaibhavkr993630-droid]

Fixes #163

Problem

In the DynamoDB view, items were displayed as raw DynamoDB-typed JSON ({"S": "Hello"}) in the items table, and the edit modal was wrong in both modes.

Cause

/api/dynamodb/tables/{name}/items (and /query) return DynamoDB-typed attributes, and the backend tests rely on that. DynamoDBBrowser treated them as plain values:

• the items table rendered JSON.stringify of the typed attribute
• the edit modal's "Plain JSON" mode showed typed data, and switching to "DynamoDB JSON" wrapped it a second time
• Delete / Delete selected wrapped the already-typed key again before sending it

Fix (frontend only, DynamoDBBrowser.tsx)

• Convert items to plain values for the items table
• Edit opens in Plain JSON, like the AWS console. Switching to DynamoDB JSON on an untouched item shows the original typed item, so sets (SS) keep their exact types
• Delete sends the typed key as returned by the API
• Reuse dynamoItemToPlainMap instead of a duplicate local decoder

Testing

• Updated the browser test mocks to the real typed response shape (the old mocks used plain values, which hid the bug) and added tests for plain display, format switching and saving without double-encoding
• tsc -b, eslint and the DynamoDB tests pass
• Checked by hand against MiniStack using the steps from the issue: the table shows Hello / 42 / ["a","b"], Edit shows plain JSON, DynamoDB JSON shows the exact typed form, and Delete removes the row

Note

Saving in Plain JSON mode still writes string sets back as lists (plain JSON has no set type). Use DynamoDB JSON mode to keep a set.

[DaviReisVieira]

Merged!! Thanks a lot for this. Reproducing first and posting the plan on the issue before opening the PR made the review easy, and swapping the test mocks to the real typed shape was the right call, the old ones were hiding the bug.

Two follow-ups, neither on you:

• I opened DynamoDB editor: saving in Plain JSON drops set, binary and large-number types #172 for the Plain JSON save losing sets, binary and large numbers. You already noted the SS case, I just want it visible.
• One small thing for next time: the table converts the whole item once per cell (dynamoItemToPlainMap(item)[key]). Converting each row once with useMemo would do the same with less work.

If #172 or #170 look fun to you, go for it!