Rename the misspelled `stmp_*` configuration options to `smtp_*`
and add a new `smtp_tls_mode` option (`starttls`, `tls`, `none`)
to control encryption when connecting to the SMTP server. Reject
credentials in plaintext mode.
Change `sqlpage.send_mail` to return its JSON argument unchanged
on success and update the example to use a local Mailpit SMTP
server via Docker Compose.
### Motivation
- Provide a built-in `sqlpage.send_mail(...)` SQL function so pages can send plain-text emails from SQL code.
- Allow the SMTP server to be configured via an environment / configuration option so the function can target a deployable SMTP endpoint.
### Description
- Added a new function implementation at `src/webserver/database/sqlpage_functions/functions/send_mail.rs` implementing `sqlpage.send_mail(json)` which accepts a JSON object with required `recipient`, `subject`, and `body` and optional `sender` and `reply_to`, sends the message and returns `sent` on success.
- Registered the function in the SQLPage function registry by adding `send_mail` to `src/webserver/database/sqlpage_functions/functions.rs`.
- Added a configuration option `stmp_host: Option<String>` to `AppConfig` in `src/app_config.rs`, with `parse_stmp_host`/`validate_stmp_host` helpers that accept either `host` or `host:port` and default to port 25 when none is provided; validation is run from `AppConfig::validate`.
- Added `lettre` to `Cargo.toml` and updated `Cargo.lock` to enable SMTP sending, and added official-site documentation and a migration at `examples/official-site/sqlpage/migrations/75_send_mail.sql` describing usage and parameters.
- Documented the `stmp_host` option in `configuration.md`.
### Testing
- Ran `cargo fmt --all`, which completed successfully.
- Ran `git diff --check` which reported no immediate style errors.
- Attempted `cargo clippy --all-targets --all-features -- -D warnings`, but it was blocked by a toolchain/build issue (a dependency `libsqlite3-sys` build script uses the unstable `cfg_select` feature) and did not complete.
- Attempted `cargo test`, but it was similarly blocked by the same `libsqlite3-sys` build-script error and did not complete.
SQLPage functions that are the whole value of a selected column now
execute after the database query, once per returned row. If the query
returns no rows, the function is not called. This ensures deterministic
behavior and prevents expensive or side-effectful operations from
running unnecessarily.
Document that the folder/destination_folder argument of
sqlpage.persist_uploaded_file must be chosen by the app author and never
derived from untrusted request data. It is joined directly to the web
root, so a value containing '..' or an absolute path would write the
uploaded file outside the web root. Docs-only clarification of existing
intended behavior; no logic change.
lovasoa