Implement auth, persistence, typed responses, and injectable RNG

Auth: JWT tokens (sb-auth) with argon2 password hashing, login/register
endpoints, Bearer token middleware protecting all routes except auth.
Authorization checks ensure users can only access their own characters.

Persistence: SQLite via rusqlite (sb-db) with write-through on all
mutations. Optional via SB_DB_PATH env var; falls back to in-memory.

Typed responses: ~20 response DTOs in sb-shared replacing ad-hoc JSON.

Combat: Injectable RNG via &mut impl Rng for deterministic tests.

Clean Architecture: Combat types and response DTOs in sb-shared; domain
services in sb-core; auth in sb-auth; persistence in sb-db.

crates/sb-core/src/songs.rs

@@ -0,0 +1,59 @@
+use serde::Serialize;
+
+#[derive(Debug, Clone, Serialize)]
+pub struct SongDef {
+    pub id: &'static str,
+    pub name: &'static str,
+    pub description: &'static str,
+    pub combat_effect: &'static str,
+    pub required_level: i32,
+}
+
+pub const BARD_SONGS: &[SongDef] = &[
+    SongDef {
+        id: "seekers_ballad",
+        name: "The Seeker's Ballad",
+        description: "Produces light while exploring and increases the party's chance to hit in combat.",
+        combat_effect: "accuracy",
+        required_level: 1,
+    },
+    SongDef {
+        id: "travellers_tune",
+        name: "The Traveller's Tune",
+        description: "Makes the party more dexterous and agile, harder to hit.",
+        combat_effect: "defense",
+        required_level: 1,
+    },
+    SongDef {
+        id: "badhr_kilnfest",
+        name: "Badh'r Kilnfest",
+        description: "An ancient Elven melody that heals wounds during combat and while traveling.",
+        combat_effect: "heal",
+        required_level: 1,
+    },
+    SongDef {
+        id: "waylands_watch",
+        name: "Wayland's Watch",
+        description: "Soothes foes, reducing the damage they deal in combat.",
+        combat_effect: "weaken",
+        required_level: 2,
+    },
+    SongDef {
+        id: "falkentyne_fury",
+        name: "Falkentyne's Fury",
+        description: "Drives the party into a berserker rage, increasing melee damage.",
+        combat_effect: "damage",
+        required_level: 3,
+    },
+    SongDef {
+        id: "lucklaran",
+        name: "Lucklaran",
+        description: "Sets up a partial anti-magic field, increasing protection against spells.",
+        combat_effect: "magic_resist",
+        required_level: 4,
+    },
+];
+
+pub fn available_songs(level: i32) -> Vec<&'static SongDef> {
+    BARD_SONGS.iter().filter(|s| s.required_level <= level).collect()
+}