[Jorl17]

This admittedly completely vibe-coded PR handles:

• Multi-language support (including changing the notification message) with English and Portuguese (European) as added languages
• Customizable notification messages
• An improved log viewer which does not choke on very large logs and supports chunked loading (and unloading)
• Is entirely backwards compatible (i.e.: literally nothing should change for old users, other than getting the new options defaulting to what they previously had)
• A very nitpicky change I just had to add: clicking the sidebar brand now takes us to the home page.
• Backend and frontend tests, as well as a GitHub Actions workflow that runs both of them.

As part of this change, notification channels get a language field (default fr) and optional subject/body overrides. The "live" preview uses the same builder as a real send (POST /api/notifications/preview).

As for the log viewer, the run detail no longer ships the entire log_output blob. Instead, GET /api/runs/{id}/logs returns a window, and the viewer jumps to start/end and loads/unloads chunks as you scroll so a huge log does not sit in memory. List/detail expose log_bytes instead.

I can't 100% confirm that the french texts were not changed during the introduction of localization, but I whipped my best whip with cursor to make sure they didn't.

Test plan (as written entirely by an LLM, and expected to be as useful they are as elbow replacements)

• First visit with no saved language follows the browser; picking one in the sidebar survives a reload
• An existing notification channel still sends the old French text until you change it
• Change a channel's language, leave templates empty, preview, then override subject/body
• Open a large finished run, jump Start / End, scroll both ways (older chunks load, far-end chunks drop)
• Click the sidebar brand from Storage or Notifications and land on Tasks
• CI is green

[Jorl17]

P.S.: Sorry for the massive diff, but I figured that since I'm running this version, might as well contribute back.

It's MUCH smaller than it looks though (a lot of that are the translation strings and adding them in the right places)!