refactor(conductor/product-guidelines.md): thin-pointer §Data Structure Conventions to type_aliases.md

Per agent_directives_consolidation_20260705 §3.4.

The 14-line §Data Structure Conventions section (the 'names for shapes'
pattern intro + the 16-alias list + canonical reference) is replaced
with a 1-line pointer to conductor/code_styleguides/type_aliases.md,
the canonical home for the 10 TypeAlias definitions + 11 per-aggregate
dataclasses + 5-pattern decision tree.

Net: 14 lines reduced to 1 line of pointer. The type-registry
auto-generation note (docs/type_registry/) is preserved as unique
project information.

Phase 3.2, 3.3, 3.4 all complete in this single commit batch.

conductor/product-guidelines.md

@@ -66,16 +66,7 @@ The canonical home (with code examples, the 5 patterns, the audit-script enforce
 
 ## Data Structure Conventions
 
-The codebase follows the "names for shapes" pattern: every `dict[str, Any]`
-or `list[dict[...]]` should use a `TypeAlias` from `src/type_aliases.py`.
-The core aliases (`Metadata`, `CommsLogEntry`, `CommsLog`, `HistoryMessage`,
-`History`, `FileItem`, `FileItems`, `ToolDefinition`, `ToolCall`,
-`CommsLogCallback`) plus the extended per-aggregate dataclasses
-(`SessionInsights`, `DiscussionSettings`, `CustomSlice`, `MMAUsageStats`,
-`ProviderPayload`, `UIPanelConfig`, `PathInfo`, `FileItemsDiff`, plus
-the `JsonPrimitive`/`JsonValue` pair) cover the common patterns. The canonical
-reference is in
-[`conductor/code_styleguides/type_aliases.md`](code_styleguides/type_aliases.md).
+The canonical home (with the 10 `TypeAlias` definitions + 11 per-aggregate dataclasses + the 5-pattern decision tree) is [`conductor/code_styleguides/type_aliases.md`](code_styleguides/type_aliases.md). This section is a 1-line pointer to that canonical home.
 
 **Field-level schema information is in `docs/type_registry/`.** This is
 auto-generated by `scripts/generate_type_registry.py` (runs as part of