feat(bridge): server id from the environment, and the first release workflow (phase 18)

Module-rust phase 18, step 3 of docs/modules/rust/PLAN.md §34.2.7.

The environment seam (D150): when the plugin writes its default config and
RUSTLINK_SERVER_ID holds a valid id (the site's ^[a-z0-9][a-z0-9-]{0,63}$),
the file's ServerId is that value. It is read nowhere else: after that write
the file is canonical and the site's lock applies. An invalid value is logged
and ignored. This is how the egg names a server; not a message change, so the
protocol stays at 12.

The release (D145, §34.2.1): release.yml reuses servuo-plugins' release engine
unchanged (tag-only, secrets preflighted, orphan tags recovered and swept, the
installer's bundle.yml dispatched at the end). The adapter re-runs
checkPlugin.js and packages runicgateway-rust-plugin-<version>.tar.gz with a
framework-neutral layout: RunicGateway.cs, its [Info] version stamped to the
release, and a manifest.json folding in overlay.toml.

overlay.toml gains min_carbon_version = "2.0.259", the build R19 was proven on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

overlay.toml

@@ -46,6 +46,17 @@ protocol = 12
 # simpler than the ServUO one.
 min_oxide_version = "2.0.7585"
 
+# ── Carbon compatibility ─────────────────────────────────────────────────────
+#
+# The same file runs unchanged on Carbon (docs/modules/rust/PLAN.md R19); the
+# installer and the egg decide whether it lands in `oxide/plugins/` or
+# `carbon/plugins/`. This is the build R19 was proven on (PLAN.md §34.4).
+#
+# Neither floor is measured from a DLL by `doctor`: a plugin that compiled and
+# connected on this framework is the fact a floor only approximates, so a
+# connected plugin is the pass, and the floors are printed with any failure.
+min_carbon_version = "2.0.259"
+
 # The `oxide/plugins/` files this overlay expects to find already installed. They
 # are not shipped here — they are third-party plugins an operator installs from
 # uMod — and the installer's `doctor` reports a missing one rather than