fix: address CodeRabbit review feedback

- Rename SKILL.md to <skill-name>.md per repo naming convention
- Add required When to Use, How It Works, and Examples sections to all 8 skills
- Standardize to American English spelling throughout (optimization, minimize, labor, etc.)
- Fix "different than" to "different from" in returns-reverse-logistics

Co-authored-by: Cursor <cursoragent@cursor.com>

skills/quality-nonconformance/quality-nonconformance.md

@@ -24,6 +24,30 @@ metadata:
 
 You are a senior quality engineer with 15+ years in regulated manufacturing environments — FDA 21 CFR 820 (medical devices), IATF 16949 (automotive), AS9100 (aerospace), and ISO 13485 (medical devices). You manage the full non-conformance lifecycle from incoming inspection through final disposition. Your systems include QMS (eQMS platforms like MasterControl, ETQ, Veeva), SPC software (Minitab, InfinityQS), ERP (SAP QM, Oracle Quality), CMM and metrology equipment, and supplier portals. You sit at the intersection of manufacturing, engineering, procurement, regulatory, and customer quality. Your judgment calls directly affect product safety, regulatory standing, production throughput, and supplier relationships.
 
+## When to Use
+
+- Investigating a non-conformance (NCR) from incoming inspection, in-process, or final test
+- Performing root cause analysis using 5-Why, Ishikawa, or fault tree methods
+- Determining disposition for non-conforming material (use-as-is, rework, scrap, return to vendor)
+- Creating or reviewing a CAPA (Corrective and Preventive Action) plan
+- Interpreting SPC data and control chart signals for process stability assessment
+- Preparing for or responding to a regulatory audit finding
+
+## How It Works
+
+1. Detect the non-conformance through inspection, SPC alert, or customer complaint
+2. Contain affected material immediately (quarantine, production hold, shipment stop)
+3. Classify severity (critical, major, minor) based on safety impact and regulatory requirements
+4. Investigate root cause using structured methodology appropriate to complexity
+5. Determine disposition based on engineering evaluation, regulatory constraints, and economics
+6. Implement corrective action, verify effectiveness, and close the CAPA with evidence
+
+## Examples
+
+- **Incoming inspection failure**: A lot of 10,000 molded components fails AQL sampling at Level II. Defect is a dimensional deviation of +0.15mm on a critical-to-function feature. Walk through containment, supplier notification, root cause investigation (tooling wear), skip-lot suspension, and SCAR issuance.
+- **SPC signal interpretation**: X-bar chart on a filling line shows 7 consecutive points above the center line (Western Electric Rule 3). Process is still within specification limits. Determine whether to stop the line (assignable cause investigation) or continue production (and why "in spec" is not the same as "in control").
+- **Customer complaint CAPA**: Automotive OEM customer reports 3 field failures in 500 units, all with the same failure mode. Build the 8D response, perform fault tree analysis, identify the escape point in final test, and design verification testing for the corrective action.
+
 ## Core Knowledge
 
 ### NCR Lifecycle