Rename replicated: true to onlyThisInstance: false (make replication opt-out by default)

The `replicated` flag in the Ops API currently means "replicate this operation to all cluster nodes". The intended default for v5.0+ is that **replication is on by default** — operators only opt out when they want a local-only operation.

## Proposed change

Rename `replicated: true` → `onlyThisInstance: false` so the semantics naturally default to "replicated":

| Old (4.x) | New (5.x) | Effect |
|---|---|---|
| *(omitted)* | *(omitted)* | Local only (4.x default) → **replicated** (5.x default) |
| `replicated: true` | `onlyThisInstance: false` | Replicated |
| `replicated: false` | `onlyThisInstance: true` | Local only |

## Back-compat requirements

- 4.x line: `replicated: true/false` continues to work as before (`false` by default = local only).
- 5.x: accept both `replicated` (deprecated alias) and `onlyThisInstance`. `onlyThisInstance: false` is the new default.
- Deprecation warning when `replicated` is used; docs updated.

## Why this matters

The current default of "local only" makes it too easy to forget `replicated: true` and silently operate on a single node. Making replication the default aligns with the platform's distributed nature.

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🤖 Filed by Claude on behalf of Kris.