feat: harden API client, align with mcp-ecosystem standards (#15)

* Add connection validation, stdio safety, and improved error handling

Introduces a new tool for validating EDD API connection, enforces MCP stdio protocol safety by redirecting console output to stderr, and adds detailed HTTP error diagnostics with actionable hints. Updates manifest and server metadata, normalizes EDD API URLs, and expands tests for error handling and stdio cleanliness. Also adds brand assets and screenshots.

* feat: harden API client, align with mcp-ecosystem standards

- Customer ID fallback logic (tries customer, id, user_id, user params)
- Robust stats date-range parsing with value coercion and range filtering
- Discount code normalization across list/get sale responses
- Add edd_validate_connection tool to README
- 3 new unit tests (26 total, all passing)

Standards alignment:
- Add eslint-config-prettier integration
- Add tsconfig strict flags (noUnusedLocals, noUnusedParameters, noImplicitReturns)
- Fix prepublishOnly to run tests before publish
- Fix ESLint errors in stdio.ts console patching
- Fix manifest.json screenshots to reference actual asset
- npm audit fix (0 vulnerabilities)

Release infrastructure:
- Release-please manifest mode with config files
- OIDC Trusted Publishing (no NPM_TOKEN needed, Node 24)
- Auto-build .mcpb Desktop Extension on release
- Slack announce job

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

* Remove README.md from assets and enhance stdio test for stderr capture

- Deleted the assets/README.md file, which contained brand asset guidelines.
- Updated the stdio-clean unit test to capture and assert stderr output, ensuring better error diagnostics during process execution.

* Enhance stdio-clean test for improved process termination handling

- Updated the `terminate` function to check for both `exitCode` and `signalCode` before returning.
- Refactored the promise handling for process exit to improve reliability.
- Adjusted the test timeout for better performance during execution.

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

chore(main): release mcp-edd 1.1.0 (#16)

Co-authored-by: Jack Arturo <johngarturo@gmail.com>