Normalize connection URLs on the read path

[kmcginnes]

Description

Follow-up to #1982, which trimmed URL whitespace only on connection-form submit — that never repairs connections already persisted with bad data. This normalizes at the read path instead, so existing connections work without being re-saved.

• normalizeConnection now strips newlines and surrounding whitespace (in addition to the existing trailing-slash) from url and graphDbUrl. Because it feeds every request and the graph-db-connection-url proxy header, existing bad data is repaired on read.
• normalizeConnection also tolerates a missing url key. Persisted configs are not schema-validated on read, so a stored connection can lack url despite the compile-time required type; previously this crashed the connection view app-wide via undefined.replace.
• Exported connection files clean the url too and omit an empty graphDbUrl, so a non-proxy export survives its own import validation.
• Export is refused with a toast when a connection has no usable URL, and "Save a Copy & Delete" now deletes only when the backup copy was actually written (previously it deleted regardless, losing the connection with no copy).

Out of scope, by design: the connection form (CreateConnection.tsx, being reworked separately), any IndexedDB migration, and Zod-on-read for stored configs.

Validation

• pnpm checks and full pnpm test pass (all suites green).
• New tests cover: whitespace/newline stripping and missing-url tolerance in normalizeConnection; clean re-importable export for both non-proxy (graphDbUrl omitted) and proxy connections; export-refused toast; and delete-skipped-when-refused in the save-a-copy flow.

How to read

1. configuration.ts — the core change: new normalizeUrl helper and its use in normalizeConnection
2. saveConfigurationToFile.ts — export cleaning + empty-graphDbUrl omission
3. exportConnection.ts — new guarded export helper returning success
4. ConnectionDeleteButton.tsx — gate the delete on a successful copy

Related Issues

• Closes Connection form accepts spaces and newlines in URL fields #1978
• Related to Normalize connection URL whitespace #1982

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.