Add email sending (service + 3 flows) and a general asset label generator

Email: a stdlib SMTP mailer (settings-first config, graceful no-op when
unconfigured), a test-email endpoint wired to the Email settings page,
forced first-login password change (users.mustchangepassword, migration
7d23, /change-password flow), new-user welcome mail, and on-demand
report/alert delivery (POST /api/reports/email + Email Report buttons)
with an external-cron-with-a-scoped-PAT path documented for automation.
All tests patch smtplib - no network.

Labels: a shared /print/asset-label/<type>/<id> view any asset detail
page opens - card or plain style, QR or barcode, configurable encoding.
Per-type qr_target_* templates plus label_default_style/codetype/encodes
settings on the Printing page. Measuring-tool labels default to encoding
their inspection-operation code (derived from the location name, e.g.
0615), so every tool in an area shares the area code - verified by
decoding the rendered QR. Machine labels default to the machine number;
blank-serial handled gracefully.

808 tests pass; both features verified live.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -12,6 +12,49 @@ ADR-007 and ADR-002.
 
 ### Added
 
+- Email sending. A stdlib-only mail service (`shopdb/utils/mailer.py`;
+  `smtplib`/`ssl`/`email`) reads the existing `email` SMTP settings
+  settings-first with an `SMTP_*` env fallback, sends multipart HTML+text, and
+  is a graceful no-op (logs a warning, returns False) when email is disabled or
+  the host is unset. The SMTP password is never logged. Three flows use it:
+  (1) New-user welcome + forced first-login password change. Admin-created users
+  (POST `/api/users`) are flagged `mustchangepassword` (new `users` column,
+  migration `7d23_user_mustchangepassword`, default false) and sent a
+  best-effort welcome email with the facility name, username, temporary
+  password, and sign-in link; the account is created even if mail fails
+  (response carries a `warning`). Login returns `mustchangepassword`; the
+  frontend forces the user through a new `/change-password` view (POST
+  `/api/auth/change-password`, jwt-guarded) before the app, and changing the
+  password clears the flag and resets lockout counters. A self-service "Change
+  password" entry is also available from the user menu.
+  (2) Test email. POST `/api/settings/test-email` (settings.edit) sends a probe
+  and surfaces any SMTP error with the password scrubbed; wires up the Email /
+  SMTP settings page "Send Test Email" button.
+  (3) On-demand alert/report delivery. POST `/api/reports/email`
+  (reports.export) mails `{subject, columns, rows}` as an HTML table to a
+  supplied recipient or the site `alert_recipients`; an "Email report" button on
+  the Warranty and Toner report pages posts the loaded rows. There is no
+  scheduler: automation is an external cron hitting the endpoint with a scoped
+  API token (PAT). Documented in `docs/CONFIG.md`.
+- Shared asset label/code generator: a single `/print/asset-label/<assettype>/<id>`
+  page (public, like the other `/print/*` routes) that any asset detail page
+  opens via a "Print Label" button (machines, computers, printers, network
+  devices, measuring tools). A no-print controls panel toggles the layout
+  (`card` badge vs `plain` code-only), the code type (QR vs CODE128 barcode),
+  and what the code encodes: the asset page link, asset number, serial number,
+  a per-type custom target template, or - for measuring tools by default - the
+  tool's inspection location code so every tool at one operation shares one
+  code (e.g. `0615`). QR codes reuse the shared logo-overlay renderer. New
+  `printing` settings seed and surface on the Printing & Labels settings page:
+  `qr_target_machine`, `qr_target_computer`, `qr_target_network_device`,
+  `qr_target_measuring_tool`; `label_default_style` (default `card`) and
+  `label_default_codetype` (default `qr`); and a per-asset-type default for what
+  the code encodes, `label_default_encodes_<type>` (machines default to their
+  machine number, measuring tools to their inspection location code, the rest to
+  a page link), all overridable on the label page itself. When the chosen field
+  has no value (e.g. serial number on an asset with none), the label states so
+  instead of rendering an empty code. Asset payloads now carry a derived
+  `locationcode` (leading token of the resolved own/inherited location name).
 - Support-team contact UX: the settings Support Teams page now manages each
   team's contacts in a per-team "Contacts (N)" modal (name, SSO, active, plus
   Add/Edit/Delete) instead of an inline row expander, and the application