dev-updater: build an app on the machine, install it on the phone

A Rust backend that discovers Android projects under configured roots,
builds one on request, and serves the APK over pinned TLS on a WireGuard
interface; an Android client that lists what is buildable, watches a build,
and installs the result. Enrolment carries the token and the CA, so the
phone trusts exactly the machine that issued it and nothing else.

`AGENTS.md` is the working guide and `README.md` the configuration
reference. The shared tunnel-and-TLS code lives in `vendor/wg-app-link`,
which ai-app uses too.

History before this point was squashed away, and a stale `config.json` went
with it: nothing had read that file since the config moved to RON outside
the checkout, and what it still held was one machine's absolute paths and
the names of projects on it.

.gitignore

@@ -0,0 +1,27 @@
+.gradle/
+build/
+app/androidApp/build/
+local.properties
+.kotlin/
+*.iml
+.idea/
+.DS_Store
+server/target/
+server/dev-updater.log
+
+# Private key material. The server keeps this in $XDG_CONFIG_HOME by
+# default; this catches a run pointed back into the repo with --certs.
+certs/
+
+# The added-apps list and the enrolled token hashes: machine-local
+# absolute paths, and whatever this particular machine has been pointed
+# at. Kept in $XDG_CONFIG_HOME by default, same as above -- this catches
+# a run with --config. Nothing here is shareable.
+config.ron
+
+# A test project fails its build while this exists; see test-projects/README.md.
+break-the-build
+
+# Dead: the live list is config.ron, kept in $XDG_CONFIG_HOME. This one was
+# an older format nothing reads, carrying one machine's absolute paths.
+config.json