Generate the TLS certificates in process

gen-dev-cert.sh is gone. The server ensures its own certificates on start,
which removes a setup step to remember, a dependency on whatever openssl
was installed, and a second place for the "which addresses?" answer to
live -- the leaf now covers every local IPv4 plus loopback and the
emulator's host alias, so nobody maintains a hardcoded IP.

The split that mattered in the script is kept and now enforced by tests:
the CA is generated once and left alone, because the app pins it and
replacing it strands every installed copy; the leaf is cheap and reissued
every start, so covering a new address is a restart. Both are written
owner-only into a directory outside the repo.

Two things the tests caught. DirBuilder's mode applies only when the
directory is created, so a directory that already existed kept whatever
permissions it had while holding a private key -- the mode is now set
explicitly, in the session directories too. And loading the leaf into the
real RustlsConfig needs the crypto provider installed, which main does but
tests don't.

Verified end to end: deleted the certs, started the server, watched it
generate a CA and warn that installed apps now pin the wrong one, rebuilt
the APK against the new CA, and reinstalled -- the emulator connects over
a certificate that never existed as a pasted constant.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

server/Cargo.toml

@@ -30,6 +30,15 @@ qrcode = { version = "0.14", default-features = false }
 # The wg0-bound listener needs the interface's address; the stdlib has no
 # getifaddrs. This is the smallest crate that wraps just that.
 if-addrs = "0.15"
+# Generates this server's TLS certificates on first start, replacing a
+# setup script that shelled out to whatever openssl happened to be
+# installed. In process means one place decides the extensions, the file
+# modes, and which addresses the leaf covers. x509-parser so the issuer is
+# read back from the CA actually on disk: reconstructing it from the same
+# parameters would work only as long as nothing ever changed them, and a
+# mismatched issuer name yields a chain that fails to validate rather than
+# anything that looks wrong at generation time.
+rcgen = { version = "0.14", features = ["pem", "x509-parser"] }
 # Outbound HTTPS for the usage endpoint. A small blocking client fits an
 # every-few-minutes poll better than pulling in reqwest's tower stack;
 # rustls-backed like the rest of the TLS here.