chore(license): switch from MIT to GPL-3.0-or-later

Adds top-level LICENSE (GPL-3.0 full text), updates README, and sets
`license = "GPL-3.0-or-later"` on all four crate manifests.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/relicario-cli/Cargo.toml

@@ -3,6 +3,7 @@ name = "relicario-cli"
 version = "0.5.0"
 edition = "2021"
 description = "CLI for relicario password manager"
+license = "GPL-3.0-or-later"
 
 [[bin]]
 name = "relicario"

crates/relicario-core/Cargo.toml

@@ -3,6 +3,7 @@ name = "relicario-core"
 version = "0.5.0"
 edition = "2021"
 description = "Core library for relicario password manager"
+license = "GPL-3.0-or-later"
 
 [dependencies]
 thiserror = "2"

crates/relicario-server/Cargo.toml

@@ -2,6 +2,8 @@
 name = "relicario-server"
 version = "0.1.0"
 edition = "2021"
+description = "Pre-receive Git hook for relicario password manager"
+license = "GPL-3.0-or-later"
 
 [dependencies]
 relicario-core = { path = "../relicario-core" }

crates/relicario-wasm/Cargo.toml

@@ -3,6 +3,7 @@ name = "relicario-wasm"
 version = "0.5.0"
 edition = "2021"
 description = "WASM bindings for relicario password manager"
+license = "GPL-3.0-or-later"
 
 [lib]
 crate-type = ["cdylib", "rlib"]