docs: add kit spec changelog and fix kits-memory directory name

Add a Changelog section at the top of the kit spec reference noting the
v0.32.0 field renames (memory -> agentContext, kind: agent -> kind:
sandbox, agent: block -> sandbox: block), which are deprecated aliases
that sbx kit validate warns on.

Also fix the per-kit directory name: v0.32.0 renamed kits-memory/ to
kits-agent-context/ (with automatic migration), which the docs had not
been updated to reflect.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dvdksn

content/manuals/ai/sandboxes/customize/kit-reference.md

@@ -27,6 +27,26 @@ my-kit/
     └── workspace/
 ```
 
+## Changelog
+
+Renamed fields are still accepted for backward compatibility, but
+`sbx kit validate` reports a deprecation warning for each, and a future
+release may stop accepting them. Update kits to the current names.
+
+### v0.32.0
+
+The following `spec.yaml` fields were renamed:
+
+| Previous       | Current          |
+| -------------- | ---------------- |
+| `memory`       | `agentContext`   |
+| `kind: agent`  | `kind: sandbox`  |
+| `agent:` block | `sandbox:` block |
+
+The per-kit directory was also renamed from `kits-memory/` to
+`kits-agent-context/`. An existing `kits-memory/` directory is migrated
+automatically the next time the sandbox starts.
+
 ## Top-level fields
 
 ```yaml
@@ -287,7 +307,7 @@ When several loaded kits declare `agentContext:` blocks, the content is split
 across files instead of being concatenated into the main one:
 
 - Each kit's agent context is written to `<kit-name>.md` in a sibling
-  `kits-memory/` directory next to the main memory file.
+  `kits-agent-context/` directory next to the main memory file.
 - The main memory file gets a `## Kits` section listing every kit with
   a pointer to its file. The section is delimited by
   `<!-- sbx:kits-section start -->` and `<!-- sbx:kits-section end -->`

content/manuals/ai/sandboxes/customize/kits.md

@@ -214,14 +214,14 @@ which determines the memory file's name.
 
 When more than one loaded kit declares an `agentContext:` block, each kit's
 content is written to its own `<kit-name>.md` file under a sibling
-`kits-memory/` directory. The main memory file gets a `## Kits` section
-that points to each kit file:
+`kits-agent-context/` directory. The main memory file gets a `## Kits`
+section that points to each kit file:
 
 ```text
 /Users/you/
-├── myproject/         # workspace
-├── AGENTS.md          # main memory file with a "## Kits" index
-└── kits-memory/
+├── myproject/              # workspace
+├── AGENTS.md               # main memory file with a "## Kits" index
+└── kits-agent-context/
     ├── ruff-lint.md
     ├── vale.md
     └── git-ssh-sign.md