[FIX/Parser] Fix invisible chars, excess newlines, and add MCP inspector script

[elydelva]

Summary

• Decode HTML-encoded invisible characters (‌,  , etc.) before the unicode strip pass in stripInvisible so they don't survive as literal strings in markdown output
• Apply stripInvisible to plainText so excess newlines (\n\n\n\n\n) are collapsed there too
• Add dev:inspect script in @mailmcp/cli and at the monorepo root to launch the MCP Inspector against the local source (bun run src/index.ts --mcp)

Test plan

• Run bun run dev:inspect from root — MCP Inspector should open
• Parse a LinkedIn/Fever-style email and verify no ‌ /   in markdown output
• Verify plainText no longer has 5+ consecutive newlines

🤖 Generated with Claude Code

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