Fix case-insensitive user email lookups

[jenewland1999]

Summary:

• add a shared helper to normalize emails and compare them case-insensitively
• switch authenticated user lookups in company, party, banking, stock, and activity flows to use the helper
• normalize new user emails before storing them and block case-only duplicate emails

Verification:

• eslint passed on the touched files
• typecheck still fails because of pre-existing missing @ajstrongdev/start-themes module/type errors in theme files
• the new Vitest test could not run in this sandbox because Vitest hit listen EPERM on ::1

[Copilot]

Pull request overview

This PR standardizes user-email handling to be case-insensitive across server flows, aiming to prevent authentication/user-lookup mismatches and block case-only duplicate emails at account creation.

Changes:

• Added shared email utilities (normalizeEmail, userEmailEquals) for normalization and case-insensitive comparisons.
• Updated multiple authenticated user lookups (middleware + banking/party/stocks/users server fns) to use the helper instead of case-sensitive or ad-hoc lower(...) comparisons.
• Normalized new user emails on insert and added a Vitest unit test for email normalization.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/middleware/auth.ts	Updates activity-tracking user update to use case-insensitive email matching.
src/lib/server/users.ts	Normalizes stored emails on create and reuses helper for email-based lookups.
src/lib/server/user-email.ts	Introduces shared normalization and Drizzle WHERE helper for email equality.
src/lib/server/user-email.test.ts	Adds unit test covering trimming/lowercasing behavior of normalization.
src/lib/server/stocks.ts	Switches several authenticated user lookups to helper (but leaves one inline lower(...) lookup).
src/lib/server/party.ts	Switches party-related email lookups to helper.
src/lib/server/banking.ts	Switches bank balance lookup to helper.

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