Add robust DB migration strategy and runtime DB pragmas (WAL, busy timeout)

[clFaster]

Goal

Add robust DB migration strategy and runtime DB pragmas (WAL, busy timeout)

Type

Technical

Effort

L

Impact

High

Evidence

DB setup currently uses basic init + single user_version handling in src-tauri/src/db.rs and only sets foreign_keys in src-tauri/src/db.rs

First Implementation Step

Introduce migration runner (v1 -> v2 -> ...) and set journal_mode=WAL, busy_timeout