[connectors] Connector framework — registry, auth, grants, scopes, tool bridge #86

[connectors] Connector framework — registry, auth, grants, scopes, tool bridge

A typed connector abstraction so a new integration is declared once, not built as bespoke routes.

Do

• Connector { id, label, auth: 'oauth'|'token'|'app', scopes: {read, write}, grantModel: 'user'|'instance-resource', tools: ToolDef[] } in a registry.
• Auth adapter reuses lib/connector-oauth.ts + user_api_keys (refresh tokens, envelope-encrypted) + github-app.ts for the App model. A connectorClient(env, provider, {userId, instanceId}) mints the access token and enforces scope.
• Grants reuse instance_connector_grants (0044) generalized beyond folders (resource_type: folder|repo|spreadsheet|…). requireConnectorGrant gates every tool call to granted resources.
• Connector → tools bridge: a connector's tools auto-register in the tool registry; they're offered to an agent only when (a) declared in capabilities.tools, (b) the subscriber has connected the provider, and (c) a grant exists (for instance-resource connectors).
• Per-instance enablement UI (console): connect provider → grant resource(s) → the connector's tools light up for that instance.

Acceptance

• A new connector added by declaring {auth, scopes, grantModel, tools} — no bespoke routes.
• Tool handlers obtain auth via connectorClient; scope + grant enforced centrally; parameterized + audited.
• Read-only connectors can't perform writes; ungranted resources rejected (403).

Depends on the tool-registry issue. Part of the connector/tool framework epic.