fix(users): normalise emails, remove demo-user fallback

[portableDD]

Closes #1575
Closes #1574
Closes #1573
Closes #1572

Summary

• User emails are not normalised, so A@x.com and a@x.com can register as separate accounts #1572: emails are trimmed and lower-cased in the register and login DTOs (@Transform) and again in UsersService.findByEmail/create, so Jane@Corp.com and jane@corp.com are the same account (duplicate registration returns 409, login is case-insensitive, forgot-password also matches). Adds migration NormaliseUserEmails that lower-cases existing rows and adds a unique index on lower(email). It aborts and lists the accounts if two existing users differ only by case, rather than merging them silently.
• GET /users/me falls back to a fake ADMIN "demo user" instead of failing #1573: removes the hard-coded ADMIN "demo user" fallback in GET /users/me; a missing user id now throws 401. Uses @GetUser('id') instead of @Req() req: any. Adds a controller spec for the missing-user case.
• Docker Compose backend cannot boot: wrong port, missing JWT_REFRESH_SECRET and a JWT secret shorter than 32 characters #1574 and Database environment variable names and defaults disagree between app, compose, CI and docs #1575 (compose/CI/database env alignment) are not implemented in this PR; only 2 of the 4 assigned issues are addressed.

Linked issues

Closes #1575, #1574, #1573, #1572 (see top of description)

Checks

• Lint passes for every area touched
• Build passes
• Tests pass
• No secrets, keys, or .env values are committed

Not run: dependencies were not installed in this workflow, so lint, build and tests were not executed. The migration has not been run against a database. Known gap: a concurrent double-registration can still hit the new unique index as a 500 rather than a 409.

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