docs(install/talos): document Talos / talosctl / Cozystack version pairing (#484)

## What

Adds a new *Version Compatibility* section to
`content/en/docs/v1/install/talos/boot-to-talos.md` spelling out which
Talos image the reader has to feed to `boot-to-talos` for a given
Cozystack release, how `talosctl` has to line up, and why the
`boot-to-talos` interactive default is *not* the right answer on its
own. Also refreshes the console-session example on the same page
(`v1.10.5` → `v1.12.6`) so it matches the pinned Talos version the rest
of the v1 docs and the Cozystack v1.2.x release profile use.

## Why

Fresh-install users in the community chat keep hitting the same version
mismatch:

- `boot-to-talos` v0.7.1 (the latest release) hard-codes its default
installer image to `ghcr.io/cozystack/cozystack/talos:v1.11.6` in
`cmd/boot-to-talos/main.go`.
- Cozystack v1.2.x pins Talos **v1.12.6** in
`packages/core/talos/images/talos/profiles/installer.yaml`, and Talm /
Helm templates target v1.12.
- `talosctl` is downloaded separately and defaults to whatever `latest`
is on siderolabs/talos (`v1.12.6` today).

If the reader follows the boot-to-talos prompts and accepts the
suggested default, they get a Talos v1.11 node under a Cozystack
installer that expects v1.12, and the bootstrap fails in obscure ways
(schedule errors, Talm template failures, nested-CRD mismatches). The
fix is trivial — type in the right image — but it is not documented
anywhere the reader would find it before running the command.

The new section:

- Lists the three moving parts (Talos / talosctl / Cozystack) in a short
compatibility table.
- Names the concrete pair for Cozystack v1.2.x (Talos `v1.12.6` +
`talosctl` v1.12.x) and links to the profile file in
`cozystack/cozystack` so a reader on a different release can look up the
same for themselves.
- Adds a warning callout that explains the boot-to-talos default is
unrelated to the Cozystack release and links directly to the `main.go`
line where the default lives.

## Verification

- Pinned Talos version confirmed against
`packages/core/talos/images/talos/profiles/installer.yaml` in
`cozystack/cozystack` at tag `release-1.2.1` (`version: v1.12.6`,
`baseInstaller.imageRef: ghcr.io/siderolabs/installer:v1.12.6`).
- `boot-to-talos` default verified via `gh search code --repo
cozystack/boot-to-talos "v1.11"`, which points at
`cmd/boot-to-talos/main.go` defaulting to
`ghcr.io/cozystack/cozystack/talos:v1.11.6`.
- `ghcr.io/cozystack/cozystack/talos:v1.12.6` existence verified via the
GHCR package API.
- `hugo` builds cleanly; the new section and refreshed example render
correctly.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated boot-to-talos documentation with version compatibility
guidance for Cozystack v1.2.x (Talos v1.12.6).
* Added warning about potential version mismatches when using default
Talos installer images.
  * Updated example logs and defaults to reflect current versions.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: kvaps

content/en/docs/v1/install/talos/boot-to-talos.md

@@ -14,6 +14,31 @@ It works entirely from userspace and has no external dependencies except the Tal
 
 Note that Cozystack provides its own Talos builds, which are tested and optimized for running a Cozystack cluster.
 
+## Version Compatibility
+
+Three versions need to line up when you install Cozystack on Talos:
+
+| Component | Where it comes from | Must match |
+| --- | --- | --- |
+| **Talos** on the node | `-image` flag passed to `boot-to-talos` | the Talos version that ships with the Cozystack release you are installing |
+| **`talosctl`** on your workstation | downloaded separately from [siderolabs/talos releases](https://github.com/siderolabs/talos/releases) | the major.minor of the Talos version you wrote to the node |
+| **Cozystack** | `--version` flag passed to `helm upgrade --install cozy-installer` | — (the anchor; everything else follows) |
+
+For **Cozystack v1.2.x** the pinned Talos version is **v1.12.6**
+([`packages/core/talos/images/talos/profiles/installer.yaml`](https://github.com/cozystack/cozystack/blob/release-1.2.1/packages/core/talos/images/talos/profiles/installer.yaml)).
+Use `ghcr.io/cozystack/cozystack/talos:v1.12.6` as the `boot-to-talos` image and download `talosctl` v1.12.x.
+
+{{% alert color="warning" %}}
+`boot-to-talos` v0.7.x carries its own hardcoded default image
+(`ghcr.io/cozystack/cozystack/talos:v1.11.6` as of v0.7.1, see
+[`cmd/boot-to-talos/main.go`](https://github.com/cozystack/boot-to-talos/blob/v0.7.1/cmd/boot-to-talos/main.go)).
+If you let the interactive prompt fall through to that default on a cluster
+you intend to run Cozystack v1.2.x, you will end up with a Talos v1.11 node
+while the Cozystack installer and Talm templates target Talos v1.12 — you
+will hit a mismatch at bootstrap time. Always type in the image matching
+your target Cozystack release (or pass `-image` on the command line).
+{{% /alert %}}
+
 ## Modes
 
 `boot-to-talos` supports two installation modes:
@@ -53,7 +78,7 @@ Mode:
   2. install – prepare the environment, run the Talos installer, and then overwrite the system disk with the installed image.
 Mode [1]: 2
 Target disk [/dev/sda]:
-Talos installer image [ghcr.io/cozystack/cozystack/talos:v1.10.5]:
+Talos installer image [ghcr.io/cozystack/cozystack/talos:v1.11.6]: ghcr.io/cozystack/cozystack/talos:v1.12.6
 Add networking configuration? [yes]:
 Interface [eth0]:
 IP address [10.0.2.15]:
@@ -62,7 +87,7 @@ Gateway (or 'none') [10.0.2.2]:
 Configure serial console? (or 'no') [ttyS0]:
 
 Summary:
-  Image: ghcr.io/cozystack/cozystack/talos:v1.10.5
+  Image: ghcr.io/cozystack/cozystack/talos:v1.12.6
   Disk:  /dev/sda
   Extra kernel args: ip=10.0.2.15::10.0.2.2:255.255.255.0::eth0::::: console=ttyS0
 
@@ -71,12 +96,12 @@ WARNING: ALL DATA ON /dev/sda WILL BE ERASED!
 Continue? [yes]:
 
 2025/08/03 00:11:03 created temporary directory /tmp/installer-3221603450
-2025/08/03 00:11:03 pulling image ghcr.io/cozystack/cozystack/talos:v1.10.5
+2025/08/03 00:11:03 pulling image ghcr.io/cozystack/cozystack/talos:v1.12.6
 2025/08/03 00:11:03 extracting image layers
 2025/08/03 00:11:07 creating raw disk /tmp/installer-3221603450/image.raw (2 GiB)
 2025/08/03 00:11:07 attached /tmp/installer-3221603450/image.raw to /dev/loop0
 2025/08/03 00:11:07 starting Talos installer
-2025/08/03 00:11:07 running Talos installer v1.10.5
+2025/08/03 00:11:07 running Talos installer v1.12.6
 2025/08/03 00:11:07 WARNING: config validation:
 2025/08/03 00:11:07   use "worker" instead of "" for machine type
 2025/08/03 00:11:07 created EFI (C12A7328-F81F-11D2-BA4B-00A0C93EC93B) size 104857600 bytes
@@ -91,7 +116,7 @@ Continue? [yes]:
 2025/08/03 00:11:07 copying from io reader to /boot/A/initramfs.xz
 2025/08/03 00:11:08 writing /boot/grub/grub.cfg to disk
 2025/08/03 00:11:08 executing: grub-install --boot-directory=/boot --removable --efi-directory=/boot/EFI /dev/loop0
-2025/08/03 00:11:08 installation of v1.10.5 complete
+2025/08/03 00:11:08 installation of v1.12.6 complete
 2025/08/03 00:11:08 Talos installer finished successfully
 2025/08/03 00:11:08 remounting all filesystems read-only
 2025/08/03 00:11:08 copy /tmp/installer-3221603450/image.raw → /dev/sda