feat(security,ci,ui): harden CI/CD, LuCI ACL, low-space updates and mobile layout

- ci: make frontend CI read-only with strict diff check and deterministic calls.json
- ci: pin external GitHub Actions in workflows to immutable commit SHAs
- ci: add openwrt-e2e blocking gate job running docker_e2e_test.sh
- fix(diagnostic): fix contstants.ts typo and update all 13 import sites
- fix(acl): remove unused /bin/busybox exec from rpcd ACL and add regression test
- feat(updates): add low-space update fallback when creating sing-box.old is impossible
- fix(routes): preserve dedicated Discord gateway subnets (162.159.128.0/21)
- feat(ui): implement responsive auto-fit grid and mobile modal viewport bounds
- test: add viewport regression test suite in vitest

.gitignore

@@ -1,6 +1,8 @@
 fe-app-tachyon/node_modules
 fe-app-tachyon/.yarn/
 fe-app-tachyon/.env
+fe-app-tachyon/.vitest/
+fe-app-tachyon/coverage/
 .DS_Store
 shellcheck-v0.10.0/
 AGENTS.md