Migrate to Ember 7.3 with Vite/Embroider and pnpm

[raucao]

Summary

Moves Hyperchannel off the classic Broccoli build (Ember 6.4 + npm) onto Ember 7.3 with Vite/Embroider and pnpm, replaces the addons removed or deprecated in Ember 7, and fixes the regressions surfaced while validating the migration. A handful of Sockethub/messaging bug fixes and a modal accessibility pass are included.

Build & tooling

• Replaced ember-cli-build.js with ember-cli-build.mjs
  (@embroider/compat compatBuild + @embroider/vite buildOnce).
• Added vite.config.mjs, babel.config.mjs, postcss.config.mjs, root
  index.html (moved from app/index.html), testem.cjs (from testem.js),
  and app/config/environment.js (via @embroider/config-meta-loader).
• app/app.js uses Resolver.withModules(compatModules); app/router.js
  uses @embroider/router.
• Raised Node requirement to >= 20.19.0.
• CI installs via pnpm/action-setup@v4 with setup-node's cache: pnpm
  and --frozen-lockfile.

Package manager: npm → pnpm

• Pinned "packageManager": "pnpm@10.32.1"; removed package-lock.json,
  added pnpm-lock.yaml.
• Scripts shelling out now use pnpm run; README.md/AGENTS.md updated.
• pnpm.ignoredBuiltDependencies: ["@parcel/watcher"] documents that its
  install script is intentionally skipped (prebuilt binary is used).
• Removed the stale Dockerfile rather than porting it.

Styling

• SCSS kept (app.scss imported from app.js); Tailwind v3 + autoprefixer
  via postcss.config.mjs; removed ember-cli-postcss,
  @csstools/postcss-sass and postcss-scss.

Dependencies replaced / removed

• ember-promise-modals → local modals service + ModalOverlay.
• ember-concurrency → guarded async action (single usage).
• ember-lifeline → native setTimeout/requestAnimationFrame with
  destroy guards.
• ember-keyboard-shortcuts → shortcut-matches util + rewritten
  keyboard-shortcuts modifier.
• consistent-color-generation (js-sha1, whose eval("require('crypto')")
  tripped Rolldown's [EVAL] warning) → app/utils/user-color.js
  (XEP-0392 via @noble/hashes + hsluv); output unchanged.
• Removed unused/build-only deps (ember-fetch, ember-sinon,
  @ember/render-modifiers, ember-auto-import, loader.js, stylelint, webpack,
  etc.); upgraded ember-autofocus-modifier, ember-truth-helpers,
  tracked-built-ins, ember-moment, @ember/test-waiters.

Embroider compatibility

• Replaced dynamic {{component ...}} with static components in
  add-chat-account.hbs, channel-container.hbs and join-channel.hbs.
• user-color tolerates missing identifiers so a malformed nickname can't
  abort a render; restored the date-headline branch.

Bug fixes

• XMPP DMs from the user list: new user-channel-id util; firstObject
  → [0] and empty-channel guards across routes/components.
• Incoming IRC DMs: skip accounts without a server when matching the
  hostname.
• IRC leave: stopped sending the invalid empty object: {} (rejected
  by Sockethub's oneOf schema) and added the leave error callback.

Modal accessibility

• New focus-trap modifier: focuses dialog content on open (first Tab →
  "Add"), traps Tab/Shift+Tab, closes on Escape, restores focus on close.
• Dialog gets role="dialog", aria-modal, aria-label; background is
  made inert while open.
• Modal repositioned to sit slightly (~6vh) above vertical center.

Tests / docs

• tests/index.html + test-helper.js on the new blueprint; testem runs
  against dist after vite build --mode development.
• Component logic behind four tests extracted into utils (factoryFor no
  longer resolves under Embroider).
• New regression tests for the fixes above.

Test plan

• pnpm test → 150 tests: 147 pass, 3 skip, 0 fail
• pnpm lint (JS, HBS, format) → clean
• pnpm build, pnpm build-prod, pnpm start → succeed

Notes / follow-ups

• TypeScript intentionally not adopted; Tailwind kept on v3.
• docs/UPGRADE_SUMMARY.md documents the full migration.

[silverbucket]

Started up and ran without any issues, LGTM