Task/Issue URL:
https://app.asana.com/1/137249556945/project/488551667048375/task/1216542927950821?focus=true
Tech Design URL (if applicable): 

### Description

Update all GitHub workflow references to
`duckduckgo/native-github-asana-sync` from `v2.0` / `v2.5.1` to
`v2.6.0`.

v2.6.0 adds @-mention forwarding for PR reviews and comments, better
error handling on task creation, and notify-release hardening.

## Steps to test

CI workflows should continue to function as before with the updated
action version.

## UI changes

None.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Workflow-only version pin and shell refactors; no app runtime or auth
logic changes, with behavior expected to stay the same aside from the
updated action release.
> 
> **Overview**
> **Standardizes CI on `duckduckgo/native-github-asana-sync@v2.6.0`**,
replacing prior `v2.0` and `v2.5.1` pins across nightly, E2E, privacy,
release, and dependency-update workflows. Step inputs and
failure/notification behavior are unchanged; workflows pick up v2.6.0
behavior (e.g. @-mention forwarding, task-creation error handling,
notify-release hardening per the PR description).
> 
> In **`ps-review-analysis.yml`**, the same Asana action bump is paired
with **`actions/checkout@v4`**, **`actions/setup-python@v5`**, and shell
steps that write to **`$GITHUB_ENV`** via grouped `{ ... }` blocks
instead of multiple separate `echo` appends.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
ca596568cf5c80e1325f97f8ba0c14e0b9db20ee. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>