Route tool defects opaquely; remove legacy envelope shim - #826

* feat(tool-result): add ToolResult union and dual-shape invoker

Adds `ToolResult<T>` / `ToolError` to @executor-js/sdk and a
`ToolResult.ok` / `ToolResult.fail` constructor pair.

Updates the sandbox tool dispatcher to accept both the new typed union
(passes through unchanged) and the legacy `{ data, error }` envelope.
The legacy branch now walks known upstream shapes (Microsoft Graph,
DealCloud, JSON:API, plain message-bearing bodies) before falling back
to a clamped JSON.stringify of the body, so structured 4xx payloads no
longer collapse to 'Tool execution failed'. The cause/defect branch
keeps its strict .message-only discipline.

* feat(plugins): emit ToolResult from openapi, graphql, mcp, google-discovery

Migrates each dynamic plugin's invokeTool to wrap its result in the
typed ToolResult<T> union. OpenAPI and Google Discovery map non-2xx
responses to ToolResult.fail with an extracted upstream message and
the raw body in error.details; 2xx responses to ToolResult.ok with
{ status, headers, data }. GraphQL maps 200-with-errors bodies to
ToolResult.fail({ code: 'graphql_errors', ... }) and bare data to
ToolResult.ok. MCP maps { isError: true } to ToolResult.fail and
content arrays to ToolResult.ok.

Static plugin tools (executor.openapi.previewSpec / addSource,
executor.graphql.addSource) now also wrap their plain values in
ToolResult.ok for shape consistency.

Updates plugin tests that asserted on the old { status, headers, data,
error } envelope or the bare MCP { content } shape. Tests that consume
the OpenAPI plugin's invocation result use the new unwrapInvocation
helper from @executor-js/plugin-openapi/testing.

* feat(tool-result): make ToolResult mandatory and route defects opaquely

Removes the legacy { data, error } envelope shim from the sandbox tool
dispatcher. The invoker now passes ToolResult<T> through unchanged and
wraps any other plain-value plugin return in ToolResult.ok so the
sandbox surface is uniform.

Plugin/infra defects no longer pass their message into the sandbox.
The dispatcher generates a short hex correlation id, logs the full
cause with that id under executor.correlation_id, and rejects with
`Internal tool error [<corrId>]`. The QuickJS bridge and the
dynamic-worker module template defensively re-stamp the same opaque
shape; the MCP host server's top-level execute failure path does the
same.

ExecutionToolError in-band messages from the execution package's
built-in validators (tools.search arg checks, etc.) are still passed
through at the QuickJS bridge so model-facing input errors keep their
useful diagnostic.

Tests:
- ToolResult.ok / fail / isToolResult constructor unit tests.
- repro tests assert structured upstream payloads now reach the
  sandbox through ToolResult.error.details (not through .message).
- leak tests pin the new invariant: plugin defects only escape as the
  opaque generic + correlation id; no token / connection string / file
  path leaks into Error.message.
- QuickJS end-to-end defect test confirms the same shape at the
  sandbox boundary.
- Cloud HTTP integration tests, MCP host tests, dynamic-worker
  invocation tests, and plugin tests updated for the new ToolResult
  wire shape and the opaque-generic defect contract.

* Fix tool result contracts