fix(tools): collapse code-mode executor to run_code for model-direct calls

wireSchemas() already advertised only run_code under mode: 'code', but the
executor resolved every call through get(), which returns the full visible
map plus the reserved transport. A model could name a native tool directly
and bypass run_code entirely. Route the execution-path lookups through a
new private resolveExecution() that applies the mode collapse at the
operation boundary: model-direct calls under 'code' may only name run_code
(UNKNOWN_TOOL otherwise), while SDK sub-dispatches (parent token set) keep
every visible tool. get()/schemas() public semantics are unchanged.

The denial happens at createExecution, before the extensible policy
pipeline — pre-execute listeners, approval ask, and guards never observe
a call that is deterministically denied. A collapsed call honors the
pre-dispatch cancellation contract, routes aborted results through the
visible tool's finalizeContent, and captures the finalizer before
argument materialization.

Regenerated docs, catalogs, graphs, scoped events, re-recorded
translation pairs, and updated test assertions.

Fixes #1815

docs/subsystems/tools.md

@@ -571,7 +571,7 @@ async execute(exec: ToolExecutionInput): Promise<ToolExecutionResult>
 
 Types: [ScopeKey](scope.md)
 
-Source: [`packages/core/tools/src/index.ts:764`](../../packages/core/tools/src/index.ts)
+Source: [`packages/core/tools/src/index.ts:762`](../../packages/core/tools/src/index.ts)
 
 <a id="tools-events"></a>