v0.7.1: Linux GLIBC 2.35 floor + scroll main window on short screens

Two user-reported issues.

=== GLIBC too new (reported via twitter) ===

Our linux-amd64 and linux-arm64 gnu builds were compiled on
ubuntu-latest (24.04, GLIBC 2.39), which means the resulting binaries
refuse to load on anything older:

  ./mhrv-rs: /lib/x86_64-linux-gnu/libc.so.6: version 'GLIBC_2.39'
    not found (required by ./mhrv-rs)

Users on Ubuntu 22.04 / Mint 21 (GLIBC 2.35) — the typical user in Iran
where this project's target audience lives, and where they can't
dist-upgrade because they're behind exactly the kind of network
restriction this tool exists to bypass — could not run the gnu builds
at all.

Fix: pin the linux-gnu matrix entries to ubuntu-22.04 runners. GLIBC
2.35 is now the minimum; binaries load on Ubuntu 22.04, Mint 21,
Debian 12, Fedora 36+, RHEL 9+ and everything newer.

Users on older distros (Ubuntu 20.04, CentOS 7) can still use the
static musl builds (mhrv-rs-linux-musl-amd64.tar.gz et al.) which
have no GLIBC dependency at all.

=== Short-screen laptops — main window content clipped (PR #6) ===

Co-authored fix from @v4g4b0nd-0x76 in PR #6 (manually applied to
avoid pulling in 400 lines of unrelated cargo-fmt churn):

- Wrap the CentralPanel body in ScrollArea::vertical()
  .auto_shrink([false; 2]) so everything stays reachable on short
  screens.
- Lower the min_inner_size from [420, 540] to [420, 400] so laptops
  with ~13" screens at default scaling can shrink the window without
  clipping UI elements.

Closes #6.

Co-authored-by: v4g4b0nd-0x76 <v4g4b0nd-0x76@users.noreply.github.com>

Cargo.lock

@@ -1317,7 +1317,7 @@ dependencies = [
 
 [[package]]
 name = "mhrv-rs"
-version = "0.7.0"
+version = "0.7.1"
 dependencies = [
  "base64 0.22.1",
  "bytes",