docs: declare readme = "README.md" for the last four crates

hive-c0re, hive-claude, hive-forge and hivectl each ship a README.md but
never declared it in their package manifest, so cargo/docs.rs metadata
did not pick it up. Every other workspace member already sets the field;
this closes the gap left after the README backfill.

hive-c0re/Cargo.toml

@@ -2,6 +2,8 @@
 name = "hive-c0re"
 edition.workspace = true
 version.workspace = true
+readme = "README.md"
+
 [lints]
 workspace = true
 

hive-claude/Cargo.toml

@@ -2,6 +2,7 @@
 name = "hive-claude"
 edition.workspace = true
 version.workspace = true
+readme = "README.md"
 
 [lints]
 workspace = true

hive-forge/Cargo.toml

@@ -2,6 +2,7 @@
 name = "hive-forge"
 edition.workspace = true
 version.workspace = true
+readme = "README.md"
 
 [[bin]]
 name = "hive-forge"

hivectl/Cargo.toml

@@ -2,6 +2,7 @@
 name = "hivectl"
 edition.workspace = true
 version.workspace = true
+readme = "README.md"
 
 [lints]
 workspace = true