Fix transaction lifecycle notifications overriding "new" status

[jbair06]

Description:
Transaction lifecycle notifications can override each other, causing users to miss new transactions. If a transaction requires 2-of-3 signatures and users B and C sign before user A sees it, user A loses the "new transaction" notification. The transaction moves silently from "new" to "ready to sign" without user A ever being notified.

Current behavior:

Tx requires 2/3 signatures (A,B,C)
→ B and C sign before A sees it
→ A sees: "Ready to sign" tab (no "new" notification)
→ A misses notification entirely

Expected behavior:

Tx requires 2/3 signatures (A,B,C)
→ B and C sign before A sees it  
→ A still sees: "New transaction" notification
→ Notification persists until A acts on it (signs, dismisses, etc.)

Root cause:

• Notification state transitions automatically (new → ready to sign)
• Once overridden, "new" notification is lost even for eligible users
• Users only see final state, not that they missed critical lifecycle events

Scope:

• Persist "new transaction" notification for eligible users until they personally act on it
• Decouple notification state from transaction lifecycle state
• Track per-user notification state independently

Acceptance criteria:

• Users see "new transaction" notification until they personally interact with it
• Notification persists even if other users advance transaction state
• 2-of-3 scenario: all 3 users see "new" notification until each acts
• Notification clears only after user action (sign, dismiss) or final state (executed, expired, canceled)
• "Ready to sign" notifications work independently of "new" notifications