feat: replace connection keys with short seed-derived rtun3 keys

Connection keys are now a ~49-char seed (rtun3.) instead of a bundled
~1740-char certificate blob. Both endpoints deterministically derive an
identical Ed25519 CA from the seed and mint ephemeral server/client leaves
at startup (keyderive.rs); the app-layer auth token is derived from the seed.
Target is passed separately on connect (resocks-style).

- connkey.rs: rtun3 seed parse/format
- keyderive.rs: CA/server/client/token derivation
- keygen takes no args; connect requires --target
- remove miniz_oxide; TLS layer unchanged
- add determinism + key-based e2e + wrong-seed-rejected tests
- update wiki, README, design spec, CI smoke

droid-wiki/reference/dependencies.md

@@ -26,9 +26,8 @@
 | `hyper-util` | 0.1 | HTTP utilities |
 | `http-body-util` | 0.1 | HTTP body utilities |
 | `tower-service` | 0.3 | Service trait (Hyper ecosystem) |
-| `base64` | 0.22 | Connection key encoding |
-| `miniz_oxide` | 0.8 | DEFLATE compression for connection keys |
-| `sha2` | 0.10 | Certificate fingerprinting |
+| `base64` | 0.22 | Connection key seed encoding |
+| `sha2` | 0.10 | Auth-token derivation from the seed |
 | `bytes` | 1 | Byte buffers for framing |
 | `futures` | 0.3 | Future utilities |
 | `url` | 2 | URL parsing |