deps: align Cargo.toml sha2 requirement with 0.11 lockfile bump

Dependabot bumped sha2 to 0.11.0 in Cargo.lock but left the manifest
requiring 0.10, so --locked builds failed on every platform. tty7's
only sha2 usage (Sha512::digest in core::keychain) is unchanged in 0.11.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.toml

@@ -38,7 +38,7 @@ serde_json.workspace = true
 # platform store (macOS Keychain / Windows Credential Manager / Linux Secret
 # Service), so no per-platform feature guards are needed.
 uuid = { version = "1", features = ["v4", "serde"] }
-sha2 = "0.10"
+sha2 = "0.11"
 keyring = "4"
 
 # Theme files. tty7 themes are authored as YAML (`~/.config/tty7/themes/*.yaml`,