refactor: fix all P0/P1/P2 bugs and architecture issues

Bug fixes (from bugs/ directory):

- Fix cross-module DB queries in 9 modules (homework, grades, parent, diagnostic, elective, proctoring, notifications, scheduling, classes) by routing through data-access functions

- Fix shared/lib <-> auth circular dependency via new session.ts module

- Fix divide-by-zero guard in grades data-access

- Fix audit export data truncation (paginated fetch for full datasets)

- Fix missing transactions in homework grading and elective lottery

- Fix missing revalidatePath in course-plans actions

- Fix frontend permission checks using requirePermission instead of requireAuth

- Fix dashboard role routing using session.user.roles

- Fix student auth pattern (migrate getDemoStudentUser to users module)

- Fix ActionState return type handling in components

Code quality fixes:

- Remove 60+ as type assertions (replace with type guards)

- Remove non-null assertions (use optional chaining or explicit checks)

- Convert dynamic imports to static imports (grades, diagnostic)

- Add React.cache() wrapping for read functions

- Parallelize independent queries with Promise.all

- Add explicit return types to 30+ arrow functions

- Replace any with unknown + type guards

- Fix import type for type-only imports

- Add Zod validation schemas for classes and diagnostic modules

- Extract duplicate code (normalizeRoleName, normalizeBcryptHash, logger IP extraction)

- Add console.error to silent catch blocks

- Fix permission naming consistency (exam:proctor_read -> exam:proctor:read)

Architecture doc sync:

- Update 004_architecture_impact_map.md and 005_architecture_data.json

- Update management-modules-audit.md for P0-7 cross-module fix

Moved deleted proctoring event route to deletes/ folder.

src/shared/lib/session.ts

@@ -0,0 +1,35 @@
+import "server-only"
+
+/**
+ * Session access single entry point (server-only).
+ *
+ * Shared/lib modules that need the current session MUST go through this
+ * module instead of importing `@/auth` directly. `@/auth` itself imports
+ * from `@/shared/lib/*`, so a static `import { auth } from "@/auth"` in
+ * shared/lib would create a module-level cycle. The dynamic import below
+ * keeps the module-loading graph acyclic while centralising session
+ * retrieval so callers depend on `@/shared/lib/session`, not `@/auth`.
+ */
+
+export type AppSession = {
+  user: {
+    id: string
+    name?: string | null
+    email?: string | null
+    role?: string
+    roles?: string[]
+    permissions?: string[]
+  }
+} | null
+
+/**
+ * Get the current NextAuth session.
+ *
+ * Uses a dynamic import to avoid a static circular dependency on
+ * `@/auth` (which itself imports from `@/shared/lib/*`). The runtime
+ * call chain is unchanged — only the module-loading graph is acyclic.
+ */
+export async function getSession(): Promise<AppSession> {
+  const { auth } = await import("@/auth")
+  return auth()
+}