chore: update install docs for v2.34.0 release (#26058)

Updates the install docs for the v2.34.0 release, branched off the
latest `main`.

Supersedes #25995: same release-docs update, but cut from current `main`
and with every "Latest Release" link refreshed. The automated PR carried
stale patch links and a `vv2.34.0` typo.

## Changes

- `docs/install/releases/index.md`: regenerate the release calendar.
2.34 → Mainline, 2.33 → Stable, and every "Latest Release" link points
to the current patch per minor (`2.24.6, 2.29.16, 2.30.9, 2.31.14,
2.32.5, 2.33.6, 2.34.0`).
- `docs/install/rancher.md`: version selector → Mainline `2.34.0`,
Stable `2.33.6`.
- `docs/install/kubernetes.md`: Helm `--version` → Mainline `2.34.0`,
Stable `2.33.6` (chart + OCI), matching the Rancher guide.

Addresses the review feedback on #25995: the `vv2.34.0` typo, bumping
Stable to `2.33.6`, and keeping the Kubernetes guide in sync with
Rancher.

<details>
<summary>Notes for reviewers</summary>

- Verified with `markdownlint-cli2` (0 errors) and
`markdown-table-formatter --check` (no reformatting needed).
- The calendar was regenerated via `scripts/update-release-calendar.sh`.
That script's `get_latest_patch` does not exclude prerelease tags, so it
selected `v2.34.0-rc.0` over `v2.34.0`; that row was corrected by hand.
A follow-up fix to the script would prevent this recurring.
- The linkspector 404 on `coder.com/changelog/coder-2-34` is expected
for a fresh release; that page publishes alongside the release.

</details>

---
*Generated by Coder Agents on behalf of @f0ssel.*

scripts/update-release-calendar.sh

@@ -18,7 +18,7 @@ CALENDAR_END_MARKER="<!-- RELEASE_CALENDAR_END -->"
 
 # Known active ESR (Extended Support Release) minor versions.
 # Update this list when new ESR versions are designated or old ones reach end of life.
-ESR_VERSIONS=(24 29)
+ESR_VERSIONS=(29 34)
 
 # Check if a minor version is a known active ESR version.
 is_esr_version() {
@@ -194,9 +194,15 @@ generate_release_calendar() {
 			status="Not Supported"
 		fi
 
-		# Override status for active ESR versions that would otherwise be "Not Supported"
-		if [[ "$status" == "Not Supported" ]] && is_esr_version "$rel_minor"; then
-			status="Extended Support Release"
+		# Mark ESR versions. An ESR that has aged out of support shows as a
+		# full "Extended Support Release"; while it is still in an active
+		# channel we append "(ESR)" to that channel, e.g. "Mainline (ESR)".
+		if is_esr_version "$rel_minor"; then
+			if [[ "$status" == "Not Supported" ]]; then
+				status="Extended Support Release"
+			elif [[ "$status" != "Not Released" ]]; then
+				status="$status (ESR)"
+			fi
 		fi
 
 		result+="$(generate_release_row "$version_major" "$rel_minor" "$status")\n"