Add optimistic mutation preconditions (#447)

[JSv4]

Closes #447.

What changed

• Added a monotonic session version that advances once per committed mutation and successful undo/redo, while failed guards, rollbacks, and no-ops leave it unchanged.
• Added reusable optimistic preconditions for expected version, anchor content hash, exact text/range, anchor kind/scope, and exact match count.
• Added structured conflict responses carrying expected/actual values, current version, and current target metadata.
• Routed the capability through the .NET ops facade, JSON/WASM bridge, npm, Python, and MCP surfaces.
• Made guarded range replacement atomic under the session mutation gate and kept MCP preview version-neutral.
• Documented the inspect/guard/mutate/retry workflow and migration-compatible optional parameters.

Validation

• Coordinator: focused DocxSessionPreconditionTests — 7/7 passed.
• Implementer: 69 focused .NET tests covering preconditions and MCP dispatch passed.
• npm TypeScript typecheck passed.
• Python precondition test passed.
• Core, WASM, Python host, and MCP server builds passed.

Review notes

The process-facing transports are serialized end-to-end: stdio and Python handle one request at a time, MCP HTTP gates complete requests, and WASM calls are synchronous. Direct .NET mutations enforce guards under the session mutation gate.