…elicitation/create)

Adds MCP elicitation to cover two wire mechanisms needed against real-world
servers, primarily our AgentCore-hosted MCP gateway:

- URL-exception mode (2025-11-25, primary): AgentCore's gateway returns
  JSON-RPC error -32042 (ErrorCode.UrlElicitationRequired) on `tools/call`
  when a tool needs out-of-band user authorization (e.g. a downstream OAuth
  consent screen the gateway can't broker inline). MCPManager.callTool now
  catches this (matching both `McpError`/`UrlElicitationRequiredError`
  instances and raw `{code: -32042}` objects from gateway proxies that don't
  preserve the SDK class), emits an `on_elicitation` SSE event so the chat UI
  renders an authorization card, and suspends via FlowStateManager exactly
  like the existing OAuth "visit a URL, get resumed" flow. When the user
  clicks "I've authorized — continue" (POST /api/mcp/elicitation/:flowId,
  action=complete), the SAME tools/call is retried once and its result
  becomes the tool result. Cancelling or a 10-minute flow timeout fails the
  tool call with the elicitation message + URL folded into the error text,
  so it still surfaces in-band to the model/user.

- Form + URL request mode (2025-06-18/2025-11-25 elicitation/create,
  secondary): declares `capabilities.elicitation = { form: {}, url: {} }` on
  the MCP client and registers a request handler via
  `MCPConnection.setElicitationHandler`, so servers can also drive elicitation
  as a server-initiated request rather than a tools/call exception. Form-mode
  requests render field inputs (string/number/boolean/enum) and resolve with
  action accept/decline; url-mode requests render the same authorization card.

Shared plumbing: a new `mcp_elicit` flow type on the existing
FlowStateManager singleton; a new `POST /api/mcp/elicitation/:flowId` route
with per-user ownership enforcement (elicitation flow IDs embed the userId
directly, unlike OAuth's one-per-server IDs, since elicitation is scoped per
tool invocation); a new `ElicitationContent`/`on_elicitation` content type
and SSE event; an `ElicitationForm` component covering both the form and
URL-card variants; and an `mcpSettings.elicitationMode` config flag forwarded
to the client.

Adapted from a fork patch (form-mode only, against an older LibreChat base)
— rebuilt the MCPManager/connection wiring against the current OBO-aware
`callTool`, and added the URL-exception path and URL elicitation/create
variant from scratch, since neither existed in the fork or upstream.

…rt errors

Observed live against AgentCore Gateway: it returns JSON-RPC errors with
a non-2xx HTTP status, so the SDK's streamable-HTTP transport throws a
StreamableHTTPError (code = HTTP status, body embedded in the message)
instead of an McpError with code -32042 — the elicitation catch never
matched and tool calls failed generically.

extractUrlElicitation() now handles both wire shapes: protocol-level
McpError/UrlElicitationRequiredError, and the HTTP-wrapped body parsed
out of the transport error message. Tests pin the exact observed wire
format, plus non-elicitation and unparseable-body negatives.

- extractUrlElicitation: parse embedded JSON-RPC bodies regardless of
  whitespace/key order instead of matching a byte-exact code literal
- connection: do not treat a 401-wrapped -32042 elicitation as an OAuth
  failure; the spurious background reconnect raced the elicitation retry
  and left a stale gateway session (-32600)
- thread serverName/toolName through the on_elicitation payload
- add AgentCore-shaped mock elicitation server (401-wrapped and 200
  JSON-RPC modes, /consent + /reset) and an integration suite driving
  the real client stack through elicit-consent-retry end to end