fix(mcp): keep wire-name server segment unambiguous for parsing

[BlueX888]

What

buildMcpToolWireName now normalizes the server segment so it can never contain __ or edge underscores: underscore runs are collapsed and leading/trailing underscores trimmed, mirroring normalizeMcpName in src/tool/builtin/mcpTool.ts. Tool names keep __ as before, since parsing splits at the first separator only.

Why

parseMcpToolWireName splits at the first __ after the mcp__ prefix, but the builder accepted server IDs containing __ — directly, via sanitization (a..b → a__b), or ending in _. Such wire names parsed back to a different server/tool pair. Reproduced on main:

buildMcpToolWireName("0__A", "a")      // => "mcp__0__A__a"
parseMcpToolWireName("mcp__0__A__a")   // => { serverId: "0", toolName: "A__a" }

With this change every built wire name parses back to a stable server/tool identity, and wire names for ordinary server IDs (including single underscores) are unchanged.

How verified

• Added tests/mcp/wire-name.spec.ts (6 cases: plain round-trip, __ in server ID, trailing underscore, sanitization-induced __, __ in tool name preserved, single underscore preserved) — all pass via tsx --test.
• Existing tests/mcp/client/McpClient.spec.ts (3 cases) still passes.
• tsc --noEmit -p tsconfig.json passes.

Fixes #424