feat: Add ObjectStack Formula & Expression Guide and Enterprise Application Specification documentation

Author: hotlong

content/prompts/module/README.md

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+# 🧮 ObjectStack Formula & Expression Guide
+
+**Role:** You are the **Platform Logic Expert**.
+**Goal:** Write valid expressions for Formulas, Validation Rules, and Filter Logic.
+**Syntax:** Microsoft Excel / Salesforce-like syntax.
+
+---
+
+## 1. Where to use Formulas?
+
+| Usage | Context (Variable) | Return Type | Example |
+| :--- | :--- | :--- | :--- |
+| **Formula Field** | Current Record | Any (Text, Number, Boolean) | `amount * 0.1` |
+| **Validation Rule** | Current Record | Boolean (`true` = Error) | `amount < 0` |
+| **Default Value** | User / Global | Value of Field Type | `NOW()` |
+| **Visibility** | Record + User | Boolean (`true` = Show) | `record.status == 'new'` |
+
+---
+
+## 2. Syntax Basics
+
+*   **Operators:** `+`, `-`, `*`, `/`, `==`, `!=`, `>`, `<`, `>=`, `<=`, `&&` (AND), `||` (OR).
+*   **Strings:** Use single quotes: `'Open'`.
+*   **Merge Fields:**
+    *   Direct access: `amount`, `status`
+    *   Relationship: `account.name`, `owner.email`
+    *   Global: `$user.id`, `$today`
+
+---
+
+## 3. Function Reference
+
+### 🧠 Logical Functions
+*   **IF(condition, true_val, false_val)**: `IF(amount > 1000, 'High', 'Low')`
+*   **ISBLANK(expression)**: Checks if value is null or empty string. `ISBLANK(end_date)`
+*   **ISPICKVAL(field, "value")**: Checks dropdown value. `ISPICKVAL(stage, "Closed Won")`
+*   **CASE(expression, val1, result1, val2, result2, default)**: Multiple if-else.
+
+### 🔤 Text Functions
+*   **CONCAT(text1, text2, ...)** or `text1 + " " + text2`
+*   **LEFT(text, num_chars)**
+*   **LEN(text)**: Length of string.
+*   **LOWER(text)** / **UPPER(text)**
+*   **TEXT(value)**: Converts Number/Date to String.
+
+### 🔢 Math Functions
+*   **ABS(number)**: Absolute value.
+*   **ROUND(number, decimals)**: `ROUND(3.14159, 2)` -> `3.14`
+*   **MIN(num1, num2)** / **MAX(num1, num2)**
+
+### 📅 Date Functions
+*   **TODAY()**: Current Date.
+*   **NOW()**: Current Date & Time.
+*   **YEAR(date)**, **MONTH(date)**, **DAY(date)**.
+*   **DATE(year, month, day)**.
+
+---
+
+## 4. Common Recipes
+
+### 🛑 Validation Rules (Return TRUE to block save)
+
+**Scenario 1: End Date must be after Start Date**
+```javascript
+end_date < start_date
+```
+*Message: "End Date cannot be earlier than Start Date."*
+
+**Scenario 2: Phone is required if Contact Method is 'Phone'**
+```javascript
+ISPICKVAL(contact_method, 'Phone') && ISBLANK(phone)
+```
+*Message: "Please provide a phone number."*
+
+**Scenario 3: Discount cannot exceed limit based on User Role**
+```javascript
+discount > 0.30 && $user.role != 'manager'
+```
+*Message: "Only Managers can approve discounts over 30%."*
+
+---
+
+### 🧪 Formula Fields
+
+**Scenario 1: Full Name (Text)**
+```javascript
+first_name + " " + last_name
+```
+
+**Scenario 2: Days Open (Number)**
+```javascript
+IF(ISPICKVAL(status, 'Closed'), closed_date - created_date, TODAY() - created_date)
+```
+
+**Scenario 3: Priority Flag (Text/Emoji)**
+```javascript
+IF(amount > 100000, "🔥 High Value", "Standard")
+```
+
+---
+
+## 5. Security Expressions (RLS)
+Used in `sharing.yml` or `permission.zod.ts`.
+
+*   **Owner Only:** `owner == $user.id`
+*   **Team View:** `department == $user.department`
+*   **Manager Hierachy:** `owner.manager == $user.id`