feat: Push Subscription keys

[s-aga-r]

ref: https://github.com/jmapio/jmap/blob/master/spec/jmap/push.mdown#pushsubscription

[Copilot]

Pull request overview

Adds support for JMAP PushSubscription encryption keys by introducing site-level key management in Mail Settings, attaching keys during push subscription creation, and decrypting inbound encrypted push notifications.

Changes:

• Add generation + validation of JMAP push encryption keys (P256DH/public, private key, auth secret) in Mail Settings with a UI action.
• Include keys in PushSubscription create payload and enforce/decrypt aes128gcm encrypted push notifications when keys are configured.
• Auto-generate keys during app install if missing.

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
mail/mail/doctype/mail_settings/mail_settings.py	Adds key validation, key generation, and helpers for base64/keypair consistency checks.
mail/mail/doctype/mail_settings/mail_settings.json	Adds new Mail Settings fields/section for JMAP Push keys.
mail/mail/doctype/mail_settings/mail_settings.js	Adds “Generate JMAP Push Keys” action with confirmation and server call.
mail/jmap/services/mail/push_subscription.py	Passes PushSubscription keys through to JMAP set/create payload.
mail/install.py	Generates site-level JMAP push keys on install when missing.
mail/client/doctype/push_subscription/push_subscription.py	Attaches keys when creating push subscriptions; adds decryption routine for encrypted notifications.
mail/api/jmap.py	Enforces encrypted push notifications when keys exist and decrypts request body accordingly.

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