feat(sync): sync both user and project workspaces automatically

.claude/plans/2026-02-03-workspace-sync-both-scopes-design.md

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+# Workspace Sync Both Scopes
+
+## Problem
+
+Users must run `workspace sync --scope user` separately to sync user-level plugins, creating friction. New users don't understand scopes and expect the command to "just work."
+
+## Design
+
+`workspace sync` syncs both user and project workspaces automatically with no `--scope` flag.
+
+### Behavior
+
+1. If `~/.allagents/workspace.yaml` exists, sync user workspace
+2. If `.allagents/workspace.yaml` exists in cwd, sync project workspace
+3. If both exist, sync both (user first, then project)
+4. If neither exists, auto-create user config via `ensureUserWorkspace()` and print:
+   "No plugins configured. Run `allagents plugin install <plugin>` to get started."
+
+### CLI Changes
+
+- Remove `--scope` / `-s` option from `workspace sync` command
+- No changes to other commands (`plugin install --scope user` etc. remain)
+
+### Output
+
+Label each sync phase. Only show phases that actually run.
+
+```
+Syncing user workspace...
+  ✓ synced 3 plugins
+Syncing project workspace...
+  ✓ synced 2 plugins
+```
+
+## Key Files
+
+- `src/cli/commands/workspace.ts` — remove `--scope` from sync command, call both sync functions
+- `src/core/sync.ts` — `syncWorkspace()` (project) and `syncUserWorkspace()` (user)
+- `src/core/user-workspace.ts` — `ensureUserWorkspace()` for auto-creation