Restructure release infra for multiple platforms; migrate real win keys

PyInstaller doesn't cross-compile and TUF metadata filenames aren't
platform-prefixed, so a shared updates/ release and repo tree can't
safely hold more than one OS's build — a second platform's publish
would silently overwrite the first's trust root and metadata.

- scripts/release/repo_init.py, repo_release.py: auto-detect platform
  (win/mac/linux) and operate inside scripts/release/<platform>/ instead
  of a flat scripts/release/ tree.
- labui.spec: bundles root.json from this platform's own tree.
- core/updater.py: points at releases/download/updates-<platform>/
  instead of a single shared updates/ tag.
- Moved the existing real keystore/repository/config (already used for
  a live Windows release) from the old flat path into
  scripts/release/win/ — same keys, same signed metadata, just
  relocated. No new keys generated, existing installs still trust it.
- .gitignore updated for the per-platform paths, plus temporary rules
  covering the old flat path during migration.
- docs/building.md, scripts/release/README.md: rewritten for the
  per-platform flow, including a note that Linux builds should happen
  on Linux/WSL2 (no cross-compiling) and that a bare .exe doesn't
  belong on the updates-<platform> release — only the TUF metadata +
  signed target archive do.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/scripts/release/win/repository/metadata/snapshot.json b/scripts/release/win/repository/metadata/snapshot.json
new file mode 100755
index 0000000..03821d1
--- /dev/null
+++ b/scripts/release/win/repository/metadata/snapshot.json
@@ -0,0 +1,19 @@
+{
+ "signatures": [
+  {
+   "keyid": "40e5301cd4b92e4a9c2e63dcca99ffa4a5627c25ac6c254f272bb52c9a076cfc",
+   "sig": "bd89d38c63ddee6537276a13657a2716a1a88346421a8d51db9fa8c12b9dc6b0db57a48bbab616930b6aaaa91c4a12a54909cd9722e07b23632638d68bd08307"
+  }
+ ],
+ "signed": {
+  "_type": "snapshot",
+  "expires": "2026-10-30T23:55:23Z",
+  "meta": {
+   "targets.json": {
+    "version": 1
+   }
+  },
+  "spec_version": "1.0.31",
+  "version": 1
+ }
+}
\ No newline at end of file