## Summary
closes https://github.com/twentyhq/core-team-issues/issues/2464
Introduces compile-time branded types to distinguish encrypted
ciphertext from plaintext strings, preventing mix-ups like the one fixed
in #20819 — but at the type level rather in addition to the one existing
at runtime.
### Branded string primitives
- Created `EncryptedString` and `PlaintextString` as hard nominal brands
using `z.string().brand(...)`, making them non-assignable to each other
or to raw `string`
- Created `isEncryptedString` type predicate to narrow `string` to
`EncryptedString` based on the `enc:v2:` envelope prefix
- Retyped `SecretEncryptionService`: `encryptVersioned` accepts
`PlaintextString`, `decryptVersioned` returns `PlaintextString`
### Entity typing
- Typed encrypted columns across entities:
`SigningKeyEntity.privateKey`,
`TwoFactorAuthenticationMethodEntity.secret`,
`ApplicationRegistrationVariableEntity.encryptedValue`,
`ApplicationVariableEntity.value`
- Parameterized JSONB types for connected account connection parameters
(`ImapSmtpCaldavParams<Pwd>`) with reusable aliases
`EncryptedImapSmtpCaldavParams` / `DecryptedImapSmtpCaldavParams`
- Typed DTOs (`CreateApplicationRegistrationVariableInput`,
`UpdateApplicationRegistrationVariablePayload`,
`UpdateApplicationVariableEntityInput`) with `PlaintextString`
### ApplicationVariable always-encrypt uniformization
- Retyped `ApplicationVariableEntity.value` to `EncryptedString | ''` —
all values are now encrypted regardless of `isSecret`
- Updated `ApplicationVariableEntityService` to always encrypt on write
and always decrypt on read
- Simplified `UpdateApplicationVariableActionHandlerService` by removing
conditional encrypt/decrypt-on-isSecret-toggle logic
- Added slow instance command (`2.9.0`) to backfill-encrypt existing
`isSecret=false` plaintext rows and tighten the `CHECK` constraint
### ConfigStorageService refactor
- Split `convertAndSecureValue` (which used `any`) into two well-typed
methods: `convertAndDecrypt` and `convertAndEncrypt`
- Introduced `isSensitiveStringValue` type predicate to narrow values
before encryption/decryption
### What's next
- Typeorm entity derivation to strictly type sitemap configuration as
code + handler logic for encryption rotation
- https://github.com/twentyhq/core-team-issues/issues/2465
