docs(web/guides): fix mailer pattern in sending-email guide to use Global.cfc factory

[wheels-bot]

The "Organize sends in app/mailers/" section of sending-email.mdx showed new wheels.Controller().sendEmail() as the mailer pattern. A bare new wheels.Controller() skips the framework's initialization path and leaves the instance without variables.params, which sendEmail() → $renderView() references in its default argument expressions — throwing on every supported engine (Component [wheels.Controller] has no accessible Member with name [PARAMS] on Lucee 7; Element PARAMS is undefined on Adobe 2023). This PR replaces both UserMailer methods with new wheels.Global().controller(name=..., params={...}).sendEmail(), the supported factory that fully wires up the instance, and adds an <Aside> warning so the correct vs incorrect pattern is explicit.

Fixes #3078

Screenshots needed

None — this is a prose and code-sample change only.

[wheels-bot]

Wheels Bot — Reviewer

TL;DR: This PR fixes the sending-email guide's broken mailer pattern — replacing new wheels.Controller().sendEmail() (which throws on every engine because a bare instance has no variables.params) with the supported new wheels.Global().controller(name, params) factory — and adds an explanatory <Aside>. I verified every technical claim against the framework source and found no blocking issues. Verdict: approve (submitted as a comment review because the PR author and this reviewer are the same bot account, and GitHub rejects self-approval).

Verified claims (evidence)

• Root cause is real. vendor/wheels/controller/rendering.cfc:575 declares string $controllerName = variables.params.controller as a default argument expression in $generateIncludeTemplatePath(), which sendEmail() reaches via $renderView() even with an absolute template= path. A bare new wheels.Controller() never populates variables.params, so the old sample throws exactly as described in #3078.
• The replacement pattern is the supported factory. vendor/wheels/Global.cfc:1209 — public any function controller(required string name, struct params = {}) — and when params is non-empty it returns $createControllerObject(arguments.params), a fully initialized instance (Global.cfc:1226-1228, Controller.cfc:13-25).
• name="UserMailer" is safe without a controller file. $objectFileName() falls back to the base Controller class when app/controllers/UserMailer.cfc doesn't exist (vendor/wheels/Global.cfc:1076-1077 — "by default we return Model or Controller so that the base component gets loaded"), so the sample won't throw a missing-component error.
• <Aside> renders. The MDX file already imports it (line 9: import { Aside, CardGrid, LinkCard } from '@astrojs/starlight/components';), and the new note matches the four existing <Aside> usages in the file.

Docs

• Changelog fragment present and correctly shaped: changelog.d/3078-sending-email-guide-mailer-factory.fixed.md (.fixed.md type, complete bullet line) — no direct CHANGELOG.md edit. ✓

Commits

• Single commit docs(web/guides): fix mailer pattern in sending-email guide to use Global.cfc factory — valid type, subject under 100 chars, DCO sign-off present. ✓

Non-blocking note

• "Fixes #3078" will close the issue, whose title also floats the alternative of hardening $renderView for out-of-request senders. The issue's own wording is "fix docs and/or harden", so a docs-only resolution is in scope — but if a maintainer wants the framework-side hardening too, it should be spun off into a follow-up issue before this merges and auto-closes #3078.

No correctness, cross-engine, security, convention, or commitlint findings. Clean docs fix, accurately evidenced.

[bpamiri]

Superseded by #3093 (merged 33ef66e, docs wave 2) — this draft branched before #3093 landed and edits the exact lines already rewritten there; develop additionally carries the richer caution Aside. No unique content to salvage.