test: add regression coverage for dotenv parse/append/remove

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Summary

Adds Vitest coverage for src/lib/dotenv-parse.ts, which backs dotenv handling in the vault file workspace and secrets tRPC routes.

Risky behavior now covered

• Parsing: blank lines, # comments, CRLF, quoted values, and lines without a valid KEY=value shape (prevents silent mis-parse of stored secrets).
• removeDotenvKey: removes assignment lines for a key while preserving comments.
• appendDotenvKey: validation for empty keys, = and # in keys, newlines in key/value, duplicate keys (aligned with parseDotenv), trailing-whitespace normalization before append, safe vs quoted formatting, and escaping of embedded " in generated lines.

Test files added/updated

• Added: src/lib/dotenv-parse.test.ts

Why this reduces regression risk

These helpers are shared across UI and API paths for .env content. Failures here corrupt stored secrets, leak wrong values, or block legitimate edits. The tests lock in the intended parse/serialize rules and error messages without coupling to React or the database.

Validation

• npm run test (all Vitest files) — pass (30 tests). Tests are pure string logic, deterministic, no network or env dependencies.