feat: add isReplay to run context (#3454)

## Summary

Adds `isReplay` boolean to the run context (`ctx.run.isReplay`),
following the same pattern as the existing `isTest`. The value is
derived from the existing `replayedFromTaskRunFriendlyId` database
field, so no schema migration is needed.

## ✅ Checklist

- [x] I have followed every step in the [contributing
guide](https://github.com/triggerdotdev/trigger.dev/blob/main/CONTRIBUTING.md)
- [x] The PR title follows the convention.
- [x] I ran and tested the code works

---

## Testing

- Verified `@trigger.dev/core` builds successfully
- Verified `webapp` typechecks successfully
- All new fields use `default(false)` for backwards compatibility

---

## Changelog

- Added `isReplay` to `TaskRun` and `V3TaskRun` schemas in `common.ts`
- Added `RUN_IS_REPLAY` semantic attribute and wired it in `taskContext`
- Propagated `isReplay` through the dequeue system, run attempt system,
and all execution context construction paths (V1 + V2)
- Added `isReplay` to `DequeuedMessage` and
`TaskRunExecutionLazyAttemptPayload` schemas
- Added patch changeset for `@trigger.dev/core`
- Updated docs: added `isReplay` to context reference, added "Detecting
replays" section to replaying page

---

💯

Link to Devin session:
https://app.devin.ai/sessions/1d6f1b3cc39a4623b72d05bf00f2d70c

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: nick <55853254+nicktrn@users.noreply.github.com>

docs/context.mdx

@@ -81,6 +81,9 @@ export const parentTask = task({
     <ResponseField name="isTest" type="boolean">
       Whether this is a [test run](/run-tests).
     </ResponseField>
+    <ResponseField name="isReplay" type="boolean">
+      Whether this run is a [replay](/replaying) of a previous run.
+    </ResponseField>
     <ResponseField name="createdAt" type="date">
       The creation time of the task run.
     </ResponseField>

docs/replaying.mdx

@@ -30,6 +30,21 @@ description: "A replay is a copy of a run with the same payload but against the
   </Tab>
 </Tabs>
 
+### Detecting replays in your task
+
+You can check if a run is a replay using the [context](/context) object:
+
+```ts
+export const myTask = task({
+  id: "my-task",
+  run: async (payload, { ctx }) => {
+    if (ctx.run.isReplay) {
+      // This run is a replay of a previous run
+    }
+  },
+});
+```
+
 ### Replaying using the SDK
 
 You can replay a run using the SDK: