feat: add entry metadata system with compile-time typed values

Add `Metadata<B>` trait and `#[metadata(Entry)]` attribute macro
to attach arbitrary, compile-time-typed metadata to entries.
Implement `ProgramCollect::get_metadata<T>()` for runtime retrieval,
backed by a global registry populated by `register_metadata!`.

Extend `pathf` with `MetadataPattern` to resolve metadata types
across modules at build time. Add two examples demonstrating
metadata usage with and without pathf integration.

1 files changed, 34 insertions, 0 deletions

diff --git a/docs/example-pages/examples.json b/docs/example-pages/examples.json
index bde9d35..31336f1 100644
--- a/docs/example-pages/examples.json
+++ b/docs/example-pages/examples.json
@@ -95,6 +95,24 @@
     ]
   },
   {
+    "id": "example-combine-pathf-metadata",
+    "name": "Pathfinder + Metadata",
+    "icon": "🧭",
+    "category": "advanced",
+    "desc": "Combines the `pathf` feature with entry metadata. The metadata `DataType` and the entry `BindType` are defined inside a submodule, and `pathf` resolves them for `gen_program!()` at build time.\n",
+    "tags": [
+      "pathf",
+      "metadata",
+      "build.rs"
+    ],
+    "files": [
+      "src/main.rs",
+      "src/sub/mod.rs",
+      "build.rs",
+      "Cargo.toml"
+    ]
+  },
+  {
     "id": "example-command-macro",
     "name": "Command Macro",
     "icon": "🚀",
@@ -254,6 +272,22 @@
     ]
   },
   {
+    "id": "example-metadata",
+    "name": "Entry Metadata",
+    "icon": "🏷️",
+    "category": "advanced",
+    "desc": "Demonstrates attaching arbitrary, compile-time-typed metadata to an entry via `#[metadata(Entry)]` and retrieving it at runtime with `ProgramCollect::get_metadata`. No `pathf` needed here — everything lives in a single module.\n",
+    "tags": [
+      "metadata",
+      "get_metadata",
+      "extras"
+    ],
+    "files": [
+      "src/main.rs",
+      "Cargo.toml"
+    ]
+  },
+  {
     "id": "example-outside-type",
     "name": "Outside Type",
     "icon": "🆕",