feat(registry): add Context7 optional API key configuration

docs/features/008-context7-auth.md

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+# Feature #008: Context7 Optional API Key Configuration
+
+## Overview
+
+Add optional API key configuration for Context7 MCP server. Context7 works without a key but has rate limits; providing a key increases quota.
+
+## Implementation Plan
+
+### Phase 1: Registry Updates
+- [ ] Update `registry/mcp-servers/context7/index.ts`
+- [ ] Add optional `configure()` lifecycle method
+- [ ] Implement optional API key prompt
+
+### Phase 2: Authentication Flow
+- [ ] Add conditional prompt for Context7 API key
+- [ ] Clearly communicate that key is optional
+- [ ] Explain benefits of providing a key (higher rate limits)
+- [ ] Store key in `.env.mcp.secrets` as `CONTEXT7_API_KEY` if provided
+- [ ] Support both configurations (with/without key)
+
+### Phase 3: Documentation
+- [ ] Update `registry/mcp-servers/context7/claude.md`
+- [ ] Document optional authentication
+- [ ] Explain rate limits and quota differences
+- [ ] Add instructions for getting an API key
+
+### Phase 4: Configuration Generation
+- [ ] Generate MCP config without env vars if no key provided
+- [ ] Generate MCP config with dotenv-cli if key provided
+- [ ] Ensure both configurations work correctly
+
+## Technical Approach
+
+```typescript
+export const context7Server: MCPServer = {
+  name: "context7",
+  displayName: "Context7",
+  description: "Up-to-date library documentation and code examples",
+
+  async configure(ctx: SetupContext): Promise<void> {
+    const useApiKey = await ctx.confirm({
+      message: "Do you want to configure a Context7 API key? (optional, provides higher rate limits)",
+      default: false
+    });
+
+    if (useApiKey) {
+      const apiKey = await ctx.prompt({
+        type: "input",
+        name: "CONTEXT7_API_KEY",
+        message: "Enter your Context7 API key (get one at https://context7.dev):"
+      });
+
+      await ctx.saveSecret("CONTEXT7_API_KEY", apiKey);
+    }
+  },
+
+  install(ctx: SetupContext): MCPConfig {
+    const hasApiKey = ctx.hasSecret("CONTEXT7_API_KEY");
+
+    if (hasApiKey) {
+      return {
+        type: "stdio",
+        command: "npx",
+        args: [
+          "-y",
+          "dotenv-cli",
+          "-e",
+          ".env.mcp.secrets",
+          "--",
+          "npx",
+          "-y",
+          "@modelcontextprotocol/server-context7"
+        ],
+        env: {}
+      };
+    } else {
+      return {
+        type: "stdio",
+        command: "npx",
+        args: ["-y", "@modelcontextprotocol/server-context7"],
+        env: {}
+      };
+    }
+  }
+};
+```
+
+## Testing Plan
+
+- Test with API key provided
+- Test without API key (skipped)
+- Test rate limits with and without key
+- Verify both MCP configurations work
+- Test library documentation lookups
+- Verify CLAUDE.md instructions are clear
+
+## Areas for Feedback
+
+1. Should we recommend getting an API key upfront?
+2. How prominently should we display rate limit information?
+3. Should we support adding a key later without re-running init?
+4. How should we handle rate limit exceeded scenarios?
+
+## Related Issues
+
+- Issue #8: https://github.com/cedric/spantree-fluent/fluent-toolkit/issues/8
+
+## References
+
+- Context7 Website: https://context7.dev
+- Context7 Docs: https://docs.context7.dev
+
+## Context7 Capabilities to Document
+
+### Library Documentation
+- `resolve-library-id`: Find Context7-compatible library ID
+- `get-library-docs`: Fetch up-to-date documentation with examples
+
+### Use Cases
+- Official framework documentation (React, Vue, Angular, etc.)
+- API reference lookup
+- Code example discovery
+- Best practices and patterns
+- Version-specific documentation
+
+### Rate Limits
+- **Without API Key**: Limited requests per IP
+- **With API Key**: Higher quota and priority access