docs: make Linux the supported release platform

Sanitized snapshot of private source e6784dc71e34681eca4ac52b0f9fe9efc9ce26ca.\n\nAI-assisted implementation reviewed by Cole Speelman.

Signed-off-by: Cole Speelman <crspeelman@gmail.com>

.gitea/workflows/cross-platform.yml

@@ -1,54 +0,0 @@
-# SPDX-License-Identifier: AGPL-3.0-only
-name: cross-platform-release-gate
-on:
-  workflow_dispatch:
-permissions:
-  contents: read
-jobs:
-  verify:
-    name: ${{ matrix.os }} / Go ${{ matrix.go }}
-    runs-on: ${{ matrix.runner }}
-    timeout-minutes: 30
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - os: Linux
-            runner: himesan-go1266
-            go: '1.26.6'
-          - os: Windows
-            runner: himesan-windows-go1266
-            go: '1.26.6'
-    steps:
-      - name: Require the repository owner on Linux
-        if: matrix.os != 'Windows'
-        run: test "$GITHUB_ACTOR" = gamertan
-      - name: Require the repository owner on Windows
-        if: matrix.os == 'Windows'
-        shell: pwsh
-        run: if ($env:GITHUB_ACTOR -ne 'gamertan') { throw 'untrusted actor' }
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
-        with:
-          fetch-depth: 0
-          persist-credentials: false
-      - name: Assert the pinned runner toolchain
-        if: matrix.os != 'Windows'
-        run: test "$(go env GOVERSION)" = "go${{ matrix.go }}"
-      - name: Assert the pinned Windows toolchain
-        if: matrix.os == 'Windows'
-        shell: pwsh
-        run: if ((& go env GOVERSION) -ne 'go${{ matrix.go }}') { throw 'unexpected Go toolchain' }
-      - name: Verify on Linux
-        if: matrix.os != 'Windows'
-        run: ./scripts/verify.sh
-      - name: Verify on Windows
-        if: matrix.os == 'Windows'
-        shell: pwsh
-        run: ./scripts/verify.ps1
-      - name: Require an unchanged checkout on Linux
-        if: matrix.os != 'Windows'
-        run: test -z "$(git status --porcelain=v1 --untracked-files=all)"
-      - name: Require an unchanged checkout on Windows
-        if: matrix.os == 'Windows'
-        shell: pwsh
-        run: if (& git status --porcelain=v1 --untracked-files=all) { throw 'dirty checkout' }