added database crate, "settings" with migrations and queries, running migrations on web startup

crates/database/readme.md

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+# sql
+
+sql interactions for ezidam
+
+the purpose of this crate is **only** to interact with the database
+
+## initial setup
+
+- install https://github.com/casey/just (it's like `make` but simpler)
+- install https://github.com/launchbadge/sqlx/tree/main/sqlx-cli (it's the tool to interact with the database)
+- install sqlite (if it is not already installed)
+- run `just create` to create an empty database
+
+## tools
+
+- `just run` to run pending migrations (in case they are not already applied)
+- `just reset` to trash the database, create a new one and apply migrations
+
+## offline
+
+### save
+
+the command `just offline` is used to verify if all sql queries are valid.
+the result will be placed in `sqlx-data.json` and is used to compile the crate. if this command fails the crate **will
+not compile**.
+
+since this command will have be executed frequently, find a way to run this command when any files are modified inside
+this crate.
+
+- vscode: TODO
+- clion: https://www.jetbrains.com/help/clion/using-file-watchers.html
+
+### check
+
+the command `just offline_check` is here to verify if offline data is up-to-date. it will return a nonzero exit
+status if data is not up-to-date.
+
+it is mainly used in CI, but you can also use it to determinate if `just offline` is required to run.
+
+## migrations
+
+### new
+
+use `just new <name>` to create a new SQL migration. the parameter `<name>` should indicate what the migration is doing.
+
+### fix mistakes
+
+if there is a mistake in the latest migration, but it has already been applied, use `just revert_last` to revert it.
+make your modifications, and run `just run` to apply it again.
+
+**note**: this works only for the most recent migration, if there is a mistake in an earlier migration, you will have to
+reset the whole database with `just reset`.
+
+consider making a new migration to fix the broken migration, and document it.
+
+## miscellaneous
+
+the command `just build_script` will create a rust build script `build.rs` to trigger recompilation when a new migration
+is added. this action can be done only at the beginning of the project.