feat(v0.5.2): cross-workspace context section in seed CLAUDE.md

Adds a concise "## Cross-Workspace Context" section to both the
task and project CLAUDE.md seed templates. Teaches the agent to
inspect related workspaces with the new commands before making
changes:

  ctask list --all          discover all workspaces, including archived
  ctask info <workspace>    view metadata and status of any workspace
  ctask notes <workspace>   read another workspace's notes.md
  ctask path <workspace>    get the filesystem path to inspect files

Closes the v0.5.2 design loop: ctask exposes workspace context
through CLI commands and lets agents consume it themselves. The
seed text is read-only by convention — the section explicitly
asks the agent to treat other workspaces as read-only unless the
user grants modification rights.

Applies to newly created workspaces only. Existing workspaces
keep their current CLAUDE.md (per spec: no retroactive overwrite).
Users with custom seed directories see this only if they update
their seeds.

internal/seed/templates.go

@@ -26,6 +26,22 @@ This is a ctask workspace. Prefer operating inside this directory unless explici
 - Record important assumptions and actions in notes.md
 - Keep the workspace root clean -- use subdirectories for organization
 
+## Cross-Workspace Context
+
+Related work may exist in other ctask workspaces. For project continuation,
+migration, debugging, or building on prior work, inspect related workspaces
+before making changes.
+
+Available commands:
+
+  ctask list --all          discover all workspaces, including archived
+  ctask info <workspace>    view metadata and status of any workspace
+  ctask notes <workspace>   read another workspace's notes.md
+  ctask path <workspace>    get the filesystem path to inspect files directly
+
+Treat other workspaces as read-only unless the user explicitly asks you to
+modify them.
+
 ## Session Handoff
 
 Before ending a session, append a brief summary to notes.md with:
@@ -84,6 +100,22 @@ Do not initialize additional git repositories inside the project subdirectory
 or any other subdirectory. If you need to check git status or make commits,
 the repo root is the workspace root.
 
+## Cross-Workspace Context
+
+Related work may exist in other ctask workspaces. For project continuation,
+migration, debugging, or building on prior work, inspect related workspaces
+before making changes.
+
+Available commands:
+
+  ctask list --all          discover all workspaces, including archived
+  ctask info <workspace>    view metadata and status of any workspace
+  ctask notes <workspace>   read another workspace's notes.md
+  ctask path <workspace>    get the filesystem path to inspect files directly
+
+Treat other workspaces as read-only unless the user explicitly asks you to
+modify them.
+
 ## Session Handoff
 
 Before ending a session, append a brief summary to notes.md with: