feat(modules): config loader refactor — YAML → DB → env pipeline

Add ModulesConfig and ModuleToggle types to config.go for explicit
module enable/disable in YAML.

Add LoadState() that merges state from three sources:
1. Backward-compat YAML fields (auth.enabled, odoo.enabled)
2. Explicit modules.* YAML toggles (override compat)
3. Database module_state table (highest precedence)

Validates dependency chain after loading. 5 loader tests.

Ref #95

internal/config/config.go

@@ -18,6 +18,25 @@ type Config struct {
 	Odoo     OdooConfig     `yaml:"odoo"`
 	Auth     AuthConfig     `yaml:"auth"`
 	Jobs     JobsConfig     `yaml:"jobs"`
+	Modules  ModulesConfig  `yaml:"modules"`
+}
+
+// ModulesConfig holds explicit enable/disable toggles for optional modules.
+// A nil pointer means "use the module's default state".
+type ModulesConfig struct {
+	Auth     *ModuleToggle `yaml:"auth"`
+	Projects *ModuleToggle `yaml:"projects"`
+	Audit    *ModuleToggle `yaml:"audit"`
+	Odoo     *ModuleToggle `yaml:"odoo"`
+	FreeCAD  *ModuleToggle `yaml:"freecad"`
+	Jobs     *ModuleToggle `yaml:"jobs"`
+	DAG      *ModuleToggle `yaml:"dag"`
+}
+
+// ModuleToggle holds an optional enabled flag. The pointer allows
+// distinguishing "not set" (nil) from "explicitly false".
+type ModuleToggle struct {
+	Enabled *bool `yaml:"enabled"`
 }
 
 // AuthConfig holds authentication and authorization settings.

internal/modules/loader.go

@@ -0,0 +1,84 @@
+package modules
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/kindredsystems/silo/internal/config"
+)
+
+// LoadState applies module state from config YAML and database overrides.
+//
+// Precedence (highest wins):
+//  1. Database module_state table
+//  2. YAML modules.* toggles
+//  3. Backward-compat YAML fields (auth.enabled, odoo.enabled)
+//  4. Module defaults (set by NewRegistry)
+func LoadState(r *Registry, cfg *config.Config, pool *pgxpool.Pool) error {
+	// Step 1: Apply backward-compat top-level YAML fields.
+	// auth.enabled and odoo.enabled existed before the modules section.
+	// Only apply if the new modules.* section doesn't override them.
+	if cfg.Modules.Auth == nil {
+		r.setEnabledUnchecked(Auth, cfg.Auth.Enabled)
+	}
+	if cfg.Modules.Odoo == nil {
+		r.setEnabledUnchecked(Odoo, cfg.Odoo.Enabled)
+	}
+
+	// Step 2: Apply explicit modules.* YAML toggles (override defaults + compat).
+	applyToggle(r, Auth, cfg.Modules.Auth)
+	applyToggle(r, Projects, cfg.Modules.Projects)
+	applyToggle(r, Audit, cfg.Modules.Audit)
+	applyToggle(r, Odoo, cfg.Modules.Odoo)
+	applyToggle(r, FreeCAD, cfg.Modules.FreeCAD)
+	applyToggle(r, Jobs, cfg.Modules.Jobs)
+	applyToggle(r, DAG, cfg.Modules.DAG)
+
+	// Step 3: Apply database overrides (highest precedence).
+	if pool != nil {
+		if err := loadFromDB(r, pool); err != nil {
+			return err
+		}
+	}
+
+	// Step 4: Validate the final state.
+	return r.ValidateDependencies()
+}
+
+// applyToggle sets a module's state from a YAML ModuleToggle if present.
+func applyToggle(r *Registry, id string, toggle *config.ModuleToggle) {
+	if toggle == nil || toggle.Enabled == nil {
+		return
+	}
+	r.setEnabledUnchecked(id, *toggle.Enabled)
+}
+
+// setEnabledUnchecked sets module state without dependency validation.
+// Used during loading when the full state is being assembled incrementally.
+func (r *Registry) setEnabledUnchecked(id string, enabled bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if m, ok := r.modules[id]; ok && !m.Required {
+		m.enabled = enabled
+	}
+}
+
+// loadFromDB reads module_state rows and applies them to the registry.
+func loadFromDB(r *Registry, pool *pgxpool.Pool) error {
+	rows, err := pool.Query(context.Background(),
+		`SELECT module_id, enabled FROM module_state`)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var id string
+		var enabled bool
+		if err := rows.Scan(&id, &enabled); err != nil {
+			return err
+		}
+		r.setEnabledUnchecked(id, enabled)
+	}
+	return rows.Err()
+}

internal/modules/loader_test.go

@@ -0,0 +1,88 @@
+package modules
+
+import (
+	"testing"
+
+	"github.com/kindredsystems/silo/internal/config"
+)
+
+func boolPtr(v bool) *bool { return &v }
+
+func TestLoadState_DefaultsOnly(t *testing.T) {
+	r := NewRegistry()
+	cfg := &config.Config{}
+
+	if err := LoadState(r, cfg, nil); err != nil {
+		t.Fatalf("LoadState: %v", err)
+	}
+
+	// Auth defaults to true from registry, but cfg.Auth.Enabled is false
+	// (zero value) and backward-compat applies, so auth ends up disabled.
+	if r.IsEnabled(Auth) {
+		t.Error("auth should be disabled (cfg.Auth.Enabled is false by default)")
+	}
+}
+
+func TestLoadState_BackwardCompat(t *testing.T) {
+	r := NewRegistry()
+	cfg := &config.Config{}
+	cfg.Auth.Enabled = true
+	cfg.Odoo.Enabled = true
+
+	if err := LoadState(r, cfg, nil); err != nil {
+		t.Fatalf("LoadState: %v", err)
+	}
+
+	if !r.IsEnabled(Auth) {
+		t.Error("auth should be enabled via cfg.Auth.Enabled")
+	}
+	if !r.IsEnabled(Odoo) {
+		t.Error("odoo should be enabled via cfg.Odoo.Enabled")
+	}
+}
+
+func TestLoadState_YAMLModulesOverrideCompat(t *testing.T) {
+	r := NewRegistry()
+	cfg := &config.Config{}
+	cfg.Auth.Enabled = true                                          // compat says enabled
+	cfg.Modules.Auth = &config.ModuleToggle{Enabled: boolPtr(false)} // explicit says disabled
+
+	if err := LoadState(r, cfg, nil); err != nil {
+		t.Fatalf("LoadState: %v", err)
+	}
+
+	if r.IsEnabled(Auth) {
+		t.Error("modules.auth.enabled=false should override auth.enabled=true")
+	}
+}
+
+func TestLoadState_EnableJobsAndDAG(t *testing.T) {
+	r := NewRegistry()
+	cfg := &config.Config{}
+	cfg.Auth.Enabled = true
+	cfg.Modules.Jobs = &config.ModuleToggle{Enabled: boolPtr(true)}
+	cfg.Modules.DAG = &config.ModuleToggle{Enabled: boolPtr(true)}
+
+	if err := LoadState(r, cfg, nil); err != nil {
+		t.Fatalf("LoadState: %v", err)
+	}
+
+	if !r.IsEnabled(Jobs) {
+		t.Error("jobs should be enabled")
+	}
+	if !r.IsEnabled(DAG) {
+		t.Error("dag should be enabled")
+	}
+}
+
+func TestLoadState_InvalidDependency(t *testing.T) {
+	r := NewRegistry()
+	cfg := &config.Config{}
+	// Auth disabled (default), but enable jobs which depends on auth.
+	cfg.Modules.Jobs = &config.ModuleToggle{Enabled: boolPtr(true)}
+
+	err := LoadState(r, cfg, nil)
+	if err == nil {
+		t.Error("should fail: jobs enabled but auth disabled")
+	}
+}