test: add unit tests for frontmatter, prefix-logger, and MCP tools

[nishant264]

This PR adds test coverage for three areas that were previously untested:

packages/shared — Frontmatter parsing (28 tests)

• Edge cases: no frontmatter, empty string, bare ---, missing closing delimiter
• Key-value pairs with whitespace, colons in values, spaces in keys
• List values and non-list indented lines
• Body extraction with leading newlines and empty body
• Frontmatter --- delimiter appearing inside body content

packages/shared — PrefixLogger (11 tests)

• Root logging with and without arguments
• Child logger delegation (1 and 3 levels deep)
• Empty prefix, special characters, sibling independence
• Root vs child isolation

packages/core — MCP builtin tools (15 tests)

• executeMcpTool: success, empty args, error surfacing, error hints
• listMcpTools: tool listing, pagination cursor, error handling
• listMcpServers: server states, empty list, error handling
• addMcpServer: valid stdio/HTTP config, schema validation errors, repo error propagation

Test results

• packages/shared: 146/146 tests passing
• packages/core: 548/548 tests passing
• Typecheck: clean in both packages

No source logic was modified — only test files were added.

[nishant264]

Hi folks! 👋 Just bumping this PR in case it got buried.

These tests add coverage for frontmatter parsing, prefix-logger, and MCP builtin tools — 39 new tests across 3 files. All passing locally (146/146 in shared, 548/548 in core). No source logic was modified.

Would love a review when anyone has time. Happy to make any changes requested!