Add connection links via a dedicated #/connect route

[kmcginnes]

Description

Lets external applications deep-link into Graph Explorer with a connection preconfigured, via a dedicated #/connect route:

#/connect?graphDbUrl=...&queryEngine=...&awsRegion=...&serviceType=...&name=...

The route resolves the params against the existing connections into one of four intents, acts on it, then redirects to the graph canvas so the connect URL never lingers in history:

• none — the params target the active connection; nothing to do.
• activate — the params match an existing connection; switch to it silently, the same no-prompt operation as clicking it in the connections list.
• create — no match; open the create form prefilled but fully editable. This is the trust gate for the untrusted endpoint details a link can carry, and the only path that can introduce a new database.
• invalid — the link's graphDbUrl failed validation; warn with a toast and ignore it.

Key design decisions:

• Auth posture is part of connection identity. Matching folds in IAM on/off (and, when on, region and service type) alongside graphDbUrl and queryEngine, so a link requesting IAM never silently reuses a plaintext connection to the same endpoint, or vice versa — a mismatch falls through to the create form.
• graphDbUrl is validated as an http(s) URL with zod; a malformed or non-http link is ignored.
• The proxy base URL is derived from document.baseURI rather than window.location.origin, so a link produces a working proxy connection on path-hosted deployments (e.g. a Neptune notebook served at /proxy/9250/explorer/ resolves the proxy to /proxy/9250).

How to read this

• Start with core/urlConnectionParams.ts — the contract core (parse / match / build / resolve) and the four-intent model.
• core/useUrlConnectionIntent.ts resolves the current route's params against live connection state.
• routes/Connect/Connect.tsx is the route that acts on the intent and redirects.
• Supporting: useActivateConnection extracted from ConnectionRow, and CreateConnection gains an initialValues prop for prefill.

Decision record in docs/adr/20260612-connection-links.md, named with the YYYYMMDD-slug ADR convention introduced separately in #1835.

Validation

• pnpm checks passes (lint, format, types).
• pnpm test / pnpm coverage green; the connect feature is covered by unit tests for the contract core, the intent hook, and the route (activate / create / none / invalid).
• Manually tested the create, silent-switch, no-op, auth-mismatch, and invalid-link flows.

Related Issues

• Replaces Feat: Activate or create connection via URL parameters #1811 — this PR supersedes the original "Activate or create connection via URL parameters" work, rebuilt on a dedicated route with auth-aware matching, URL validation, and the path-aware proxy base.
• Related to Unify Docker image by removing SageMaker variant #1773 — when the connection model drops the explicit proxy url in favor of always-relative requests, the document.baseURI derivation here becomes unnecessary and links inherit that behavior. The ADR notes this.
• Depends on Adopt date-prefixed ADR filenames #1835 — the ADR file added here follows the date-prefixed naming convention established by that PR.

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.