release: produce a versioned per-browser artifact and pin the Chrome extension id (closes #310)

manifest/chrome.json now carries a fixed public key, so the extension id and the chrome.storage.local partition holding the wallet stay stable across checkout moves and re-clones instead of being derived from the absolute path. A release entrypoint produces a self-contained versioned artifact per browser, including the files that sit at dist/ root outside both browser directories. One version source of truth, enforced: the build fails naming the culprit when the two manifests and package.json disagree, and BUILD_COMMIT now marks a dirty tree as dirty. Firefox ships an unsigned XPI; the README states that release Firefox and ESR refuse it, that Developer Edition or Unbranded is required, and that Remove is irreversible except from the recovery phrase, which is asserted by test.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: bootstrap setup install test test-e2e test-e2e-firefox lint fmt fmt-check check check-censored docker hooks build build-debug vendor-blocklist clean dev
+.PHONY: bootstrap setup install test test-e2e test-e2e-firefox lint fmt fmt-check check check-censored docker hooks build build-debug package vendor-blocklist clean dev
 
 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -41,6 +41,9 @@ check:
 check-censored:
 	@script/check-censored
 
+package:
+	@script/package
+
 docker:
 	@script/docker
 
@@ -102,7 +105,7 @@ vendor-blocklist:
 	@script/vendor-blocklist
 
 clean:
-	@rm -rf dist/
+	@rm -rf dist/ release/
 
 dev:
 	@echo "Building in watch mode..."