Add Firefox extension, Mattermost plugin, downloads page, and CI release workflow

[Copilot]

Extends TrustVault with a Firefox-compatible addon, a Mattermost right-sidebar plugin, a downloads page on the site, and a GitHub Actions workflow that auto-packages all addons on tagged releases. Also shifts the Docker server host port from 5000 → 4523.

Docker

• docker-compose.yml: server host port 5000:5000 → 4523:5000; CLIENT_URL made env-overridable

Chrome/Firefox Extensions

• All hardcoded localhost:5000 refs updated to localhost:4523 (App.jsx, background.js, manifest.json)
• Added extension/public/manifest.firefox.json — MV2 manifest with browser_action, background.scripts, and browser_specific_settings.gecko (ID trustvault@trustvault.app, min Firefox 109)
• vite.config.js updated to support --mode firefox, writing output to dist-firefox/ and overwriting manifest.json via closeBundle hook
• New build:firefox and build:all scripts in extension/package.json

Mattermost Plugin (mattermost-plugin/)

Webapp-only plugin (no server component) that registers a lock icon in the channel header; clicking it opens the RHS panel.

mattermost-plugin/
├── plugin.json                         # manifest + ServerURL config setting
└── webapp/
    ├── webpack.config.js               # Mattermost externals (React, ReactDOM, Redux)
    └── src/
        ├── index.jsx                   # registers header button + RHS component
        └── components/
            ├── TrustVaultIcon.jsx      # lock SVG for channel header
            └── TrustVaultSidebar.jsx   # login → vault list → credential reveal + copy

The sidebar stores token and apiUrl in localStorage; server URL is user-configurable via a settings panel (defaults to http://localhost:4523).

Downloads Page

• client/src/pages/DownloadsPage.jsx — three addon cards (Chrome, Firefox, Mattermost) each with a download button linking to GitHub Releases, compat badges, and collapsible step-by-step install instructions
• Route /downloads added inside the protected Layout; "Downloads" nav item added to the sidebar

CI — .github/workflows/build-extensions.yml

Triggers on v* tags; four jobs:

Job	Output
build-chrome	trustvault-chrome-<tag>.zip
build-firefox	trustvault-firefox-<tag>.zip
build-mattermost	trustvault-mattermost-<tag>.tar.gz
release	GitHub Release with all three as attached assets

All checkouts use fetch-depth: 0 to ensure tag metadata is available.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.