docs: correct miden-client pin referenced in miden-client-cli skill

[alituzun]

The miden-client-cli skill says project-template pins miden-client = "0.14":

.claude/skills/miden-client-cli/SKILL.md:49
Follow the canonical in-repo references on `0xMiden/miden-client` (the active
line, which matches project-template's pinned `miden-client = "0.14"`).

integration/Cargo.toml on main pins 0.15:

miden-client = { version = "0.15", features = ["tonic"] }
miden-client-sqlite-store = { version = "0.15", package = "miden-client-sqlite-store" }
miden-standards = { version = "0.15", features = ["testing"] }
miden-testing = "0.15"

The skill exists to send an agent to the right upstream reference, so the stale
number points it at the wrong SDK line. This changes that one occurrence to
0.15; grep -rn '0\.14' finds no others outside Cargo.lock.

Docs only, no code change.

🤖 Generated with Claude Code