Extension zips: 404 instead of SPA fallback; clear errors in packaging ...

A missing zip used to fall through try_files to index.html and download
as a 'broken archive'. /ext/* is now real files only, and package.mjs
fails early with a hint when zip or the built dist is missing.

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

Download page: extension install guide for Chrome and Firefox ...

- public /download page (nav item «Расширение»): per-browser download
  buttons and step-by-step install instructions, setup (server URL is
  the panel's own origin) and hotkey reference, en/ru
- npm run package -w @ltt/extension zips dist/{chrome,firefox} into
  packages/web/public/ext (stable names, manifest at archive root so
  "Load unpacked" works right after unpacking)
- make ext / make prod always build fresh zips; deploy/.env.example
  seeds the release address bugtrail.gnexus.space

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

v0.1.0-beta: production transfer guide and parameterized prod stack ...

- docker-compose.prod.yml reads POSTGRES_PASSWORD, HTTP(S)_PORT and
  SITE_ADDRESS from .env; caddy persists its config in a volume
- Caddyfile takes the site address from the environment — a DNS name
  turns on automatic HTTPS
- README: full first-transfer, domain/HTTPS, update and backup guide

Smoke-tested locally: fresh postgres migrates on boot, panel + /api
serve from one origin, SPA fallback works.

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

Extension: picker, note composer, recorder + infra (Makefile, prod compose, README) ...

- MV3 extension for Chrome and Firefox: single codebase, per-entry IIFE
  builds (background / content / options), manifests generated per target
- Background service worker owns all networking (Bearer token from
  storage.local), captureVisibleTab (windowId!), recorder event buffer
  with offset_ms and auto-screenshots on clicks
- Content overlay in a closed shadow root (constructable stylesheets,
  kit CSS fetched from assets/style.css with /assets URL rewrite);
  PickerLayer, NoteComposer (autofocus, Ctrl+Enter submit),
  RecorderBar (step counter, note, stop)
- Options page: server URL, login, default project
- Recorder steps link screenshots by uploaded file id (server accepts
  attachment id or file id); environment/element JSONB serialized with
  mode="json" (datetime captured_at broke inserts)
- e2e harness: headless Chromium + extension, note + recording flows
- Makefile, docker-compose.prod.yml (caddy :8081 + static panel),
  deploy/Caddyfile, README (ru) with extension install and /assets notes

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