fix(crx): enforce ToolDefinition.parameters at runtime via schema-driven validation

[Postroggy]

Summary

Closes architectural problem E in docs/architectural-improvements-todo.md.

The parameters field on every ToolDefinition carries a full JSON schema (type, required, minimum, maximum, enum, minItems, maxItems, maxLength, minLength), but the schema was only used to generate the definition sent to the LLM. The runtime path went through coerceToolInputTypes (pageToolsSupport/helpers.ts:91-113), which only did string→number / string→boolean coercion. There was no range check, no enum check, no required-field check, no length check.

Concretely: a model could pass duration: 999 to the computer wait action (declared maximum: 30) and the bad value would flow straight into the CDP layer. Same for text being too long, coordinate with fewer than 2 items, etc.

What changed

• New validateToolInput(toolName, input, toolDefinitions) function in pageToolsSupport/helpers.ts. Schema-driven so any new constraint added to a tool's parameters declaration is automatically enforced at runtime. Recurses one level into nested properties / items for common shapes.
• Call it in core.ts#executeTool dispatch, immediately after coerceToolInput and before tool.execute(). Failures return createErrorResponse with the aggregated error list.
• Tolerates missing / wrong-shape / unknown tool input — schema-driven enforcement when we have a schema, conservative passthrough otherwise.
• 22 new unit tests in validateToolInput.test.ts

Verification

• typecheck: 9 errors (unchanged from baseline, all in ContentBlocksRenderer.tsx — unrelated)
• unit tests: 172/172 passed (+22 new, was 150/150)
• build: clean
• lint: 51 errors / 175 warnings (unchanged from baseline)

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