Fix Documenter.jl build errors: docstrings, @ref links, and missing docs

- Add docstrings to get_attributes and set_attributes! for both
  ZarrsArray and ZarrsGroup
- Fix broken @ref links: "Icechunk documentation" -> "Icechunk Integration"
  in getting_started.md and cloud.md
- Add Storage and Internals sections to api.md to include all documented
  symbols (ZarrsStorageHandle, ZarrsArrayHandle, ZarrsGroupHandle,
  Base.keys, Base.getindex, create_storage, julia_shape, zarrs_subset,
  build_v3_metadata, build_v2_metadata, numpy_dtype_str)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jhamman

docs/src/api.md

@@ -15,6 +15,8 @@ zinfo
 ```@docs
 ZarrsGroup
 zgroup
+Base.keys(::ZarrsGroup)
+Base.getindex(::ZarrsGroup, ::AbstractString)
 ```
 
 ## Attributes
@@ -72,3 +74,22 @@ Zarrs.Icechunk.delete_tag
 Zarrs.Icechunk.lookup_branch
 Zarrs.Icechunk.lookup_tag
 ```
+
+## Storage
+
+```@docs
+Zarrs.create_storage
+Zarrs.ZarrsStorageHandle
+Zarrs.ZarrsArrayHandle
+Zarrs.ZarrsGroupHandle
+```
+
+## Internals
+
+```@docs
+Zarrs.julia_shape
+Zarrs.zarrs_subset
+Zarrs.build_v3_metadata
+Zarrs.build_v2_metadata
+Zarrs.numpy_dtype_str
+```

docs/src/cloud.md

@@ -18,7 +18,7 @@ subset = z[1:10, 1:10]
 ## Icechunk (S3, GCS, Azure)
 
 For cloud storage with versioning, use the Icechunk integration. See the
-[Icechunk documentation](@ref) for full details.
+[Icechunk Integration](@ref) for full details.
 
 ```julia
 using Zarrs

docs/src/getting_started.md

@@ -132,7 +132,7 @@ session = writable_session(repo, "main")
 snapshot_id = commit(session, "initial data")
 ```
 
-See the [Icechunk documentation](@ref) for full details on storage backends,
+See the [Icechunk Integration](@ref) page for full details on storage backends,
 credentials, branches, and tags.
 
 ## DiskArrays Integration

src/array.jl

@@ -250,11 +250,21 @@ end
 # Attributes
 # ---------------------------------------------------------------------------
 
+"""
+    get_attributes(z::ZarrsArray) -> Dict{String,Any}
+
+Return the array's user attributes as a dictionary.
+"""
 function get_attributes(z::ZarrsArray)
     json_str = LibZarrs.zarrs_array_get_attributes(z.handle.ptr)
     return JSON.parse(json_str)
 end
 
+"""
+    set_attributes!(z::ZarrsArray, attrs::Dict)
+
+Replace the array's user attributes and persist to storage.
+"""
 function set_attributes!(z::ZarrsArray, attrs::Dict)
     LibZarrs.zarrs_array_set_attributes(z.handle.ptr, JSON.json(attrs))
     LibZarrs.zarrs_array_store_metadata(z.handle.ptr)

src/group.jl

@@ -100,11 +100,21 @@ end
 # Group attributes
 # ---------------------------------------------------------------------------
 
+"""
+    get_attributes(g::ZarrsGroup) -> Dict{String,Any}
+
+Return the group's user attributes as a dictionary.
+"""
 function get_attributes(g::ZarrsGroup)
     json_str = LibZarrs.zarrs_group_get_attributes(g.handle.ptr)
     return JSON.parse(json_str)
 end
 
+"""
+    set_attributes!(g::ZarrsGroup, attrs::Dict)
+
+Replace the group's user attributes and persist to storage.
+"""
 function set_attributes!(g::ZarrsGroup, attrs::Dict)
     LibZarrs.zarrs_group_set_attributes(g.handle.ptr, JSON.json(attrs))
     LibZarrs.zarrs_group_store_metadata(g.handle.ptr)