Fix SMTP auth: settings tab saved wrong config keys

The Settings → E-mailrapport tab (scheduler.js) saved the SMTP username
as `user` and TLS flag as `starttls`, but every backend reader expects
`username`/`use_tls` (routes/email.py). Result: username was always
empty, server.login() was skipped, and the SMTP server rejected the
send — surfacing as a misleading "authentication failed" message even
with a valid App Password. The bug was latent because Graph is preferred
whenever M365 is connected, so the SMTP path was rarely exercised.

- scheduler.js: send/load canonical keys (username, use_tls). The
  send-report modal (scan.js) already used these.
- _load_smtp_config(): normalise legacy user→username / starttls→use_tls
  so configs saved before the fix work without re-entry.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

routes/CLAUDE.md

@@ -68,6 +68,8 @@ Exception hierarchy (all inherit `M365Error(Exception)`):
 - **Graph preferred over SMTP** — `smtp_test` and `send_report` try `_send_email_graph()` first; fall back to SMTP only if Graph raises. If Graph fails and no SMTP host saved, the Graph exception surfaces directly.
 - **Auto-email after manual scan** — `_maybe_send_auto_email()` in `routes/scan.py` called from the `_run()` thread after `run_scan()` returns. Reads `smtp_cfg.get("auto_email_manual")`; no-ops if false, no flagged items, or no recipients.
 - **Gmail vs Google Workspace** — auth error handlers check if SMTP username ends in `@gmail.com`/`@googlemail.com`; custom domains are treated as Google Workspace and error message points to the Workspace admin console.
+- **Canonical SMTP config keys are `username` and `use_tls`** — all backend readers (`smtp_test`, `_send_report_email`, `_send_email_graph`) use these. The Settings → E-mailrapport tab (`scheduler.js`) historically saved `user`/`starttls`, which left `username` empty so `server.login()` was skipped and the server rejected the send. Frontend now sends the canonical keys, and `_load_smtp_config()` normalises legacy `user`→`username` / `starttls`→`use_tls` for already-saved configs. The send-report modal (`scan.js`) already used the canonical keys. Keep both UIs and the backend on `username`/`use_tls`.
+- **Graph 202 ≠ delivered** — `_send_email_graph` returns on Graph's HTTP 202 (queued), and `smtp_test`/`send_report` treat that as success and never fall back to SMTP. A recipient on a domain Exchange Online considers an accepted/internal domain (e.g. a Google-hosted subdomain of the O365 domain) is silently dropped after the 202. There is no in-app fix for that routing; reaching such recipients requires SMTP (e.g. Google Workspace `smtp.gmail.com`/`smtp-relay.gmail.com`) or fixing Exchange Accepted Domains.
 
 ## Scheduler — scan_scheduler.py + routes/scheduler.py