release: package the extension, pin the Chrome extension id, and prove the wallet survives a reinstall (closes #310)

There was no packaging target anywhere, no artifact, and no `key` in
`manifest/chrome.json` — so an unpacked Chrome load derived its extension
id, and therefore its `chrome.storage.local` partition, from the absolute
checkout path. Moving or re-cloning the checkout presented an empty
wallet, with no error and nothing in the UI to say so.

`manifest/chrome.json` now carries a fixed `key`: the public half of an
RSA keypair, which pins the extension id to
`gipbhkogfopeahplcjhipkgpcimdpkip`. The private half is a credential and
is not in this repo; no target generates one into the working tree, and
`tests/extensionId.test.js` fails if a `.pem` is ever committed. Changing
`key` changes the id and orphans every wallet stored under the old one.

`make package` (script/package) runs `make build` — the only audited path
to a release build — and writes one self-contained, versioned archive per
browser into `release/`, plus `SHA256SUMS`. The archives are deterministic:
entries sorted, timestamps fixed, compression level fixed, so two builds
of one commit are byte-identical. Self-containment is checked rather than
assumed: every path the manifests and the popup HTML reference is resolved
and required to be inside the archive, a reference that climbs out of the
extension root is a hard failure, and files left at the `dist/` root —
`dist/styles.css`, which build.js copies into each browser directory — are
reported as deliberately not shipped rather than dropped by a glob. The
archive is then read back off disk and compared member by member against
the directory it was built from. The zip writer and reader are stdlib zlib
in `script/lib/zip.js`; no new dependency, and nothing unpinned.

One version, enforced rather than generated. `script/lib/version.js`
requires `package.json`, `manifest/chrome.json` and `manifest/firefox.json`
to agree and fails the build naming each file and what it said, instead of
reading from one of the three. `BUILD_COMMIT` now carries `-dirty` when the
working tree does not match `HEAD`, and `-unknown` when git cannot say;
the full hash behind the About screen's commit link stays clean so the link
still resolves.

Two real-browser observations, both run through the pinned harnesses:

- `tests/e2e/storagePartition.js` loads the build from two different paths
  in one Chrome profile. With `key`: same id, and the second load reads the
  first load's storage. Without `key`: different ids, and the second load
  sees an empty partition. Loading both keyed copies at once yields one id,
  not two.
- `tests/e2e/firefox/reinstall.js` installs the packaged XPI in a real
  Firefox, creates a wallet, quits the browser, restarts on the same
  profile, adds the add-on again, and decrypts the vault back to the
  original recovery phrase. It then observes that an explicit uninstall
  DESTROYS that storage — correct browser behaviour, but for a wallet it
  means Remove is irreversible except from the recovery phrase, so
  README.md says so.

Firefox ships an UNSIGNED XPI. README.md states plainly that release
Firefox and ESR will refuse it, that Developer Edition, Nightly or an
Unbranded build is required, and that a temporary add-on does not survive
a browser restart. AMO signing, CRX packing, tagging and any upload are
deliberately out of scope.

TODO.md

@@ -84,6 +84,40 @@ but the review is broader than any of them.
   lists (`src/shared/transactions.js`) keep the unfloored rule, which is out of
   scope by the issue's definition of done. `README.md`'s Display Consistency
   section records the exception.
+- 2026-08-23: The extension can be installed once and kept
+  ([#310](https://git.eeqj.de/sneak/AutistMask/issues/310)). There was no
+  packaging target anywhere, no artifact, and `manifest/chrome.json` carried no
+  `key` — so an unpacked Chrome load derived its extension id, and therefore its
+  `chrome.storage.local` partition, from the absolute checkout path: moving or
+  re-cloning the checkout presented an empty wallet with no error. The manifest
+  now carries a fixed `key` (public half only; the private half is a credential
+  and is not in this repo, and no target generates one into the tree), pinning
+  the id to `gipbhkogfopeahplcjhipkgpcimdpkip`. `make package` produces
+  `release/autistmask-chrome-<version>.zip` and
+  `release/autistmask-firefox-<version>.xpi` plus `SHA256SUMS`,
+  deterministically and via `make build` so the archives can only be made from a
+  `dist/` already verified against that build's receipt as a release build;
+  every path the manifests and the popup HTML reference is resolved and required
+  to be inside the archive, and the archive is read back off disk and compared
+  member by member — `dist/styles.css` sits at the `dist/` root outside both
+  browser directories and is reported as deliberately not shipped rather than
+  dropped by a glob. One version: `script/lib/version.js` fails the build when
+  `package.json` and the two manifests disagree, instead of reading from one of
+  them. `BUILD_COMMIT` now carries `-dirty` when the working tree does not match
+  `HEAD` (and `-unknown` when git cannot say), while the full hash behind the
+  About screen's commit link stays clean so the link still resolves. Two real
+  browser observations back it: `tests/e2e/storagePartition.js` loads the
+  extension from two different paths in one Chrome profile with and without
+  `key` and records what each does, and `tests/e2e/firefox/reinstall.js`
+  installs the packaged XPI in a real Firefox, creates a wallet, restarts the
+  browser on the same profile, adds the add-on again and decrypts the vault back
+  to the original recovery phrase — and then observes that an explicit uninstall
+  DESTROYS that storage, which is correct browser behaviour but means Remove is
+  irreversible for a wallet, now stated in README.md. Deliberately not done: AMO
+  signing, CRX packing, tagging and any upload — the Firefox artifact is
+  UNSIGNED and README.md now states that release Firefox and ESR refuse it, that
+  Developer Edition or an Unbranded build is required, and that a temporary
+  add-on does not survive a browser restart.
 - 2026-08-20: A second extension page can no longer silently delete a wallet
   ([#304](https://git.eeqj.de/sneak/AutistMask/issues/304)). `saveState()` wrote
   the entire state blob, and every extension page — the toolbar popup, a dApp