feat: add GitHub Copilot prompt support

Adds GitHub Copilot VS Code instruction and prompt files for ECC workflows, with VS Code prompt frontmatter/settings aligned to current docs and tests covering the surface.

Co-authored-by: Girish Kanjiyani <girish.kanjiyani5040@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/prompts/code-review.prompt.md

@@ -0,0 +1,56 @@
+---
+agent: agent
+description: Comprehensive code quality and security review of the selected code or recent changes
+---
+
+# Code Review
+
+Review the selected code (or the current diff if nothing is selected) across four dimensions. Only report issues you are **confident about** — flag uncertainty explicitly rather than guessing.
+
+## Dimensions
+
+### 1. Security (CRITICAL — block ship if found)
+- Hardcoded secrets, tokens, API keys, passwords
+- Missing input validation or sanitization at system boundaries
+- SQL/NoSQL injection risk (string interpolation in queries)
+- XSS risk (unsanitized HTML output)
+- Auth/authz checks missing or client-side only
+- Sensitive data in logs or error messages exposed to clients
+- Missing rate limiting on public endpoints
+
+### 2. Code Quality (HIGH)
+- Mutation of existing state instead of creating new objects
+- Functions over 50 lines or files over 800 lines
+- Nesting deeper than 4 levels
+- Duplicated logic that should be extracted
+- Misleading or non-descriptive names
+
+### 3. Error Handling (HIGH)
+- Silently swallowed errors (`catch {}`, empty catch blocks)
+- Missing error handling at async boundaries
+- Errors returned but not checked by callers
+- User-facing error messages leaking internal details
+
+### 4. Test Coverage (MEDIUM)
+- Missing tests for new logic
+- Tests that only test happy paths (missing error/edge cases)
+- Assertions that always pass
+
+## Output Format
+
+For each issue found:
+
+```
+**[CRITICAL|HIGH|MEDIUM|LOW]** — [File:Line if known]
+Issue: [What is wrong]
+Fix: [Concrete suggestion]
+```
+
+End with a summary:
+```
+## Summary
+- Critical: N
+- High: N
+- Medium: N
+- Approved to ship: yes / no (fix CRITICAL and HIGH first)
+```