docs: note that beta.1 waits for the Chromium roll (#54649)

* docs: note beta.1 waits for the Chromium roll

The Releases WG moved alpha-to-beta promotion to release automation,
gated on the release branch's Chromium reaching the version in Chrome's
Beta channel. beta.1 is no longer a fixed date, so stop listing it as one
of our solid release dates and note it can land a few days late.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

* docs: explain beta.1 delay without roll jargon

Say plainly that beta.1 can be late when the release branch has not yet
been updated to the Chromium Beta-channel version, instead of referring
to "our Chromium roll" without explaining it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

* docs: link Chrome's Beta channel in release timeline

Link to Chromium's release channel page and briefly explain that the
Beta channel is where each Chrome version is tested for about four weeks
before stable.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

* docs: clarify which release dates are fixed

Replace "our solid release dates" with plain wording: alpha.1 and stable
ship on the scheduled dates, while the prereleases in between, including
beta.1, don't have fixed dates.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

* docs: tighten beta.1 timing note

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

* docs: use canonical Chrome release channels URL

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmPhpNhEFuPd7juZ3fc781

---------

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

docs/tutorial/electron-timelines.md

@@ -12,8 +12,8 @@ This document focuses on the release cadence and version support policy.
 [Electron's Release Schedule](https://releases.electronjs.org/schedule) lists a schedule of Electron major releases showing key milestones including alpha, beta, and stable release dates, as well as end-of-life dates and dependency versions.
 
 > [!IMPORTANT]
-> Electron's official support policy is the latest 3 stable releases. Our stable
-> release and end-of-life dates are determined by Chromium, and may be subject to
+> Electron's official support policy is the latest 3 stable releases. Our beta,
+> stable, and end-of-life dates are determined by Chromium, and may be subject to
 > change. While we try to keep our planned release and end-of-life dates frequently
 > updated here, future dates may change if affected by upstream scheduling changes,
 > and may not always be accurately reflected.
@@ -48,10 +48,15 @@ gantt
 **Notes:**
 
 * Alphas are generally less stable than beta releases. The cutoff between the two
-  corresponds to when the underlying Chromium version enters Chrome's Beta channel.
-* The `-alpha.1`, `-beta.1`, and `stable` dates are our solid release dates.
+  corresponds to when the underlying Chromium version enters Chrome's
+  [Beta channel](https://www.chromium.org/getting-involved/chrome-release-channels/), where Google
+  tests each Chrome version for about four weeks before releasing it to stable.
+* `-alpha.1` and stable releases are published on the dates listed in the schedule.
+  The prereleases in between, including `-beta.1`, don't have fixed dates.
+* `-beta.1` is released automatically once the release branch is on that Chromium
+  version. This is usually the scheduled date, but it can be a few days later.
 * We strive for weekly alpha/beta releases, but we often release more than scheduled.
-* All dates are our goals but there may be reasons for adjusting the stable deadline, such as security bugs.
+* All dates are our goals but there may be reasons for adjusting them, such as security bugs.
 
 **Historical changes:**
 

docs/tutorial/electron-versioning.md

@@ -153,8 +153,8 @@ gitGraph
     cherry-pick id:"fix-1" tag:"v42.0.0-alpha.2"
 ```
 
-The version of Chromium that powers Electron 42 hits Chrome's beta channel. The `alpha` line is
-promoted to `beta`.
+The version of Chromium that powers Electron 42 hits Chrome's beta channel. Once Electron 42's
+Chromium version has caught up, the `alpha` line is promoted to `beta`.
 
 ```mermaid
 gitGraph