Simplify ConnectionConfig — remove url and proxyConnection

[kmcginnes]

Parent PRD

• Parent Simplify client-server relationship by removing proxy URL from connection config #1618

What to build

Remove url and proxyConnection from ConnectionConfig and NormalizedConnection types. Make graphDbUrl required. Simplify normalizeConnection to remove the proxy inference logic. Update fetchDatabaseRequest/getAuthHeaders to always send proxy headers (graph-db-connection-url, db-query-logging-enabled) unconditionally.

This is the core type change that cascades through the codebase, eliminating conditional branches around proxy vs direct connections.

Type: HITL — requires review before completion.

Acceptance criteria

• ConnectionConfig no longer has url or proxyConnection fields
• graphDbUrl is required on ConnectionConfig
• NormalizedConnection reflects the simplified type
• normalizeConnection no longer infers proxyConnection
• getAuthHeaders always sends graph-db-connection-url and db-query-logging-enabled headers
• All type errors resolved across the codebase
• Tests for normalizeConnection updated
• Tests for fetchDatabaseRequest/getAuthHeaders verify headers are always sent

Blocked by

• Blocked by Create apiBase module and wire client fetch to /api/* #1621

User stories addressed

• User story 10
• User story 15