feat: hostname-aware window title (#82)

Set the browser tab title to codeman:${hostname} instead of the bare
"Codeman" literal. Useful for users running multiple Codeman instances
across hosts (laptop, dev box, NAS) — the OS hostname disambiguates
which tab points at which backend.

Implementation:

- src/cli.ts: new --title-hostname <hostname> flag overrides the
  detected hostname (handy for cosmetic naming or when os.hostname()
  returns something noisy).
- src/web/server.ts: WebServer now accepts an optional titleHostname
  constructor arg (defaults to os.hostname()), composes
  windowTitle = codeman:${titleHostname}, and serves / and
  /index.html by templating that title into the cached index.html
  template (with HTML escaping of the title text).
- src/web/public/notification-manager.js: title-flash logic now uses
  this.originalTitle instead of the hardcoded "Codeman" literal, so
  the tab flash respects the per-host title.
- scripts/browser-comparison.mjs + test/file-link-click.test.ts:
  expectations updated from === "Codeman" to a startsWith("codeman:")
  predicate so they pass regardless of host.

The new index.html templating is intentionally narrow — it only
substitutes the <title> tag and continues to serve everything else
from the static template. No JS-side title injection, so it works
without JavaScript and shows the correct title from the very first
paint.

Note: test/file-link-click.test.ts shows ~49 prettier-reformat lines
that are not part of the feature — they are pre-existing prettier
debt that the pre-commit hook required me to clear. The single
behavioral change is the browserAvailable line.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>