fix: correct history token counts, project grouping, and MCP tool rows

[stefanprodan]

Three fixes to the history (h) view:

• Token overcount: Claude Code writes each content block of a message (thinking, text, tool_use) as its own entry, each repeating the message's usage. Count a message once by its id: input once, output at its final value, one turn. Tool calls still count from every block.
• Projects swallowed by a parent dir: a single session started in a parent directory (e.g. an org dir holding every repo) made every repo beneath it fold into that one row. Only fold child paths that have no sessions of their own.
• Duplicate MCP rows: one server installed both standalone and as a plugin shortened to the same server:tool label but ranked as separate rows. Sum counts per displayed label.