release: 0.1.3 — add a2amcp bin, sync server/cli version from package.json

Adds an "a2amcp" bin (alongside the existing "a2a-mcp" for back-compat)
so that npx -y a2amcp resolves the binary by package name. Without it
npx fell back unreliably when no bin matched.

Also rips the hardcoded "0.1.0" out of cli.ts and gateway.ts and reads
the version from package.json — that was why serverInfo lagged behind
the published tag. Renames the user-facing command in help / error
strings / README from a2a-mcp to a2amcp; the legacy bin stays for
existing scripts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/credentials.ts

@@ -1,7 +1,7 @@
 /**
  * Reader for ~/.a2a/credentials.json — same file the Python `a2a` CLI writes.
  *
- * We deliberately *only read* this file (and overwrite it on `a2a-mcp login`)
+ * We deliberately *only read* this file (and overwrite it on `a2amcp login`)
  * so a single login flow is shared between the Python and Node tooling.
  */
 import { promises as fs } from "node:fs";