fix(mcp): report the running instance's version, not a PATH binary (closes #1353)

@corylanou is already working on this.

Since Jul 16, 2026.

## Problem

Two distinct "versions" are wrong/conflated in the MCP server today, and #1353 is about the first:

1. **The `litestream_version` tool** execs whatever `litestream` is on `$PATH` (`cmd/litestream/mcp.go:250`). It should report the version of the **Litestream instance the MCP server represents / is connected to** — i.e. the running daemon — not an unrelated binary that happens to be first on `$PATH`. This is #1353.
2. **The MCP server's own handshake identity** is hardcoded `"1.0.0"` (`cmd/litestream/mcp.go:33`), unrelated to the real build.

These must not be conflated:
- *"What Litestream instance am I talking to?"* (version of the daemon being operated on) → **tool result**.
- *"What build is running the MCP server component?"* → **MCP handshake identity**.

They happen to coincide **today** only because the MCP server runs **embedded inside the `replicate` daemon process** (`cmd/litestream/replicate.go:184-189`): the in-process build `Version` (`cmd/litestream/main.go:40`) equals the daemon's version, which the daemon already reports over IPC (`server.go:511` sets `InfoResponse.Version = s.Version`, wired at `replicate.go:306`).

## Fix (current embedded architecture)

- `litestream_version` returns the running instance's version from the same source the daemon reports it — in-process `Version` (== `s.Server.Version` == `/info`'s `InfoResponse.Version`) — with **no exec**.
- Set the MCP server handshake version in `server.NewMCPServer` to the real build `Version` instead of `"1.0.0"`.

## Future (standalone / remote) — cross-ref only, out of scope here

Once the MCP server can run **standalone** (#1370) or against a **remote daemon** (#1367), the MCP process is no longer the daemon and the two versions diverge. In that mode the tool must source the instance version from the **connected daemon over IPC** (`/info` → `InfoResponse.Version`, `server.go:509,538-544`), not from the MCP process's own binary (it may additionally surface the MCP server's own build for diagnostics). Those issues own that mechanism; this issue fixes the embedded case and must not bake in an assumption that blocks it.

## Acceptance

- `litestream_version` reports the running instance's version with no subprocess, matching `litestream version` of the daemon build.
- The MCP handshake advertises the real build version, not `"1.0.0"`.
- Closes #1353.

## Cross-refs

Sole owner of the #1353 version bug. #1367 (in-process refactor) converts the **other** tools and must not touch/reintroduce version reporting; #1367 and #1370 own the remote/standalone "connected-daemon version" behavior described above.