v1.2.5: CI self-hosted apt-lock fix (v1.2.4 release was incomplete)

v1.2.4 tagged cleanly but its CI failed — parallel Linux matrix jobs
on the self-hosted runners all raced on `/var/lib/apt/lists/lock` and
failed the `sudo apt-get install` step within ~20s. v1.2.4's release
job therefore skipped and no assets were published.

Fix:

- Pre-installed every apt dependency the workflow needs on both
  self-hosted runners (eframe system libs, gcc-aarch64-linux-gnu,
  gcc-arm-linux-gnueabihf).
- Seeded per-runner cargo linker configs at
  /home/ghrunner/cargo-{01,02}/config.toml so the "echo
  [target.xxx] linker = ..." workflow step is also unnecessary.
- Gated the "Install Linux eframe system deps" and the two cross-
  compile-toolchain steps on `runner.environment == 'github-hosted'`
  so only hosted runners call apt-get; self-hosted runners skip the
  whole thing and use pre-installed tooling.

Re-tagging as v1.2.5 since v1.2.4 is an abandoned tag (git tag exists
but no GitHub Release was cut for it).

Same code changes as what v1.2.4 was meant to ship: PR #78 range-
parallel validation, PR #79 port-collision rejection, README note
on Android 7+ user-CA trust.

.github/workflows/release.yml

@@ -112,11 +112,12 @@ jobs:
           key: ${{ matrix.target }}
 
       # eframe needs a few system libs on Linux for window management, keyboard,
-      # and OpenGL/X11/Wayland. On self-hosted these persist across runs so this
-      # is a no-op after the first time; on GH-hosted macOS/Windows the step
-      # is guarded out anyway.
+      # and OpenGL/X11/Wayland. Gated to GitHub-hosted runners only — the
+      # self-hosted runners pre-install all of these once at setup time, and
+      # letting multiple parallel matrix jobs race on `sudo apt-get install`
+      # fights over /var/lib/apt/lists/lock and fails them all.
       - name: Install Linux eframe system deps
-        if: runner.os == 'Linux'
+        if: runner.os == 'Linux' && runner.environment == 'github-hosted'
         run: |
           sudo apt-get update
           sudo apt-get install -y \
@@ -126,8 +127,13 @@ jobs:
             libx11-dev \
             libgl1-mesa-dev libglib2.0-dev libgtk-3-dev
 
+      # Cross-compile toolchains. Same story as above — gated to hosted
+      # runners; self-hosted has gcc-aarch64-linux-gnu + gcc-arm-linux-gnueabihf
+      # pre-installed, and the linker entries live in
+      # /home/ghrunner/cargo-{01,02}/config.toml (seeded once at runner
+      # setup time, picked up via CARGO_HOME env).
       - name: Install aarch64 cross-compile toolchain (Linux only)
-        if: matrix.target == 'aarch64-unknown-linux-gnu'
+        if: matrix.target == 'aarch64-unknown-linux-gnu' && runner.environment == 'github-hosted'
         run: |
           sudo apt-get update
           sudo apt-get install -y gcc-aarch64-linux-gnu
@@ -135,7 +141,7 @@ jobs:
           echo 'linker = "aarch64-linux-gnu-gcc"' >> ~/.cargo/config.toml
 
       - name: Install armhf cross-compile toolchain (Linux only)
-        if: matrix.target == 'arm-unknown-linux-gnueabihf'
+        if: matrix.target == 'arm-unknown-linux-gnueabihf' && runner.environment == 'github-hosted'
         run: |
           sudo apt-get update
           sudo apt-get install -y gcc-arm-linux-gnueabihf