chore(cleanup): remove 4 unused .socket/* constants

`DEFAULT_BLOB_FOLDER`, `DEFAULT_PACKAGES_FOLDER`, `DEFAULT_DIFFS_FOLDER`,
and `DEFAULT_SOCKET_DIR` had zero callers anywhere in the
workspace. The paths they encoded (`.socket/blob`,
`.socket/packages`, `.socket/diffs`, `.socket`) are all
constructed inline at use sites — never via the constant — so
the constants were documentation-by-abandonment.

`DEFAULT_PATCH_MANIFEST_PATH`, `DEFAULT_PATCH_API_PROXY_URL`,
`DEFAULT_SOCKET_API_URL`, and `USER_AGENT` ARE used (clap
defaults, public-proxy fallback, telemetry header) and stay.

Workspace test sweep stays green (118 + 414 lib tests).

Assisted-by: Claude Code:claude-opus-4-7

Author: mikolalysenko

crates/socket-patch-core/src/constants.rs

@@ -1,18 +1,6 @@
 /// Default path for the patch manifest file relative to the project root.
 pub const DEFAULT_PATCH_MANIFEST_PATH: &str = ".socket/manifest.json";
 
-/// Default folder for storing patched file blobs.
-pub const DEFAULT_BLOB_FOLDER: &str = ".socket/blob";
-
-/// Default folder for storing per-package patched archives (tar.gz).
-pub const DEFAULT_PACKAGES_FOLDER: &str = ".socket/packages";
-
-/// Default folder for storing per-file diff blobs (bsdiff format).
-pub const DEFAULT_DIFFS_FOLDER: &str = ".socket/diffs";
-
-/// Default Socket directory.
-pub const DEFAULT_SOCKET_DIR: &str = ".socket";
-
 /// Default public patch API URL for free patches (no auth required).
 pub const DEFAULT_PATCH_API_PROXY_URL: &str = "https://patches-api.socket.dev";