fix(web): start a new preset blank instead of copying the default

Copying is already its own action, offered on the row being copied, so the two
routes now arrive at the same editor by whichever one the author chose. **New
preset** starting from some preset nobody named put a composition in the editor
that the author had to recognise as unwanted before deleting it — and the
preset it copied was the deployment default, which is the one least likely to
be what someone reaching for "new" wanted.

A blank draft has no source, so it names none and makes no read: the editor's
"copied from" line and header clause appear only when there is a source.

packages/client/ui-agent-preset/tests/section-store.spec.ts

@@ -239,16 +239,18 @@ describe('opening a composition', () => {
 })
 
 describe('creating a preset', () => {
-  it('copies the default composition when no source is named', async () => {
-    const { controller } = harness()
+  it('starts blank when no source is named', async () => {
+    const { controller, calls } = harness()
     await controller.load()
+    const before = calls.length
 
     await controller.createFrom()
 
-    // The default is the composition a new session gets, so it is the one
-    // worth starting from — and a copy is writable wherever it came from.
-    expect(draftOf(controller)).toMatchObject({ id: '', source: 'standard', creating: true, writable: true })
-    expect(draftOf(controller).content).toBe('- id: tool-bash\n')
+    // Copying is its own action on the row being copied, so this one is a copy
+    // of nothing: no source to name, and no read to make.
+    expect(draftOf(controller)).toMatchObject({ id: '', creating: true, writable: true, content: '' })
+    expect(draftOf(controller).source).toBeUndefined()
+    expect(calls).toHaveLength(before)
   })
 
   it('copies a named preset', async () => {
@@ -260,12 +262,12 @@ describe('creating a preset', () => {
     expect(draftOf(controller)).toMatchObject({ source: 'mine', creating: true, content: '- id: tool-read\n' })
   })
 
-  it('does nothing before the roster loaded', async () => {
+  it('opens the blank editor without the roster, which it no longer reads', async () => {
     const { controller, calls } = harness()
 
     await controller.createFrom()
 
-    expect(controller.store.getSnapshot().draft).toBeNull()
+    expect(draftOf(controller)).toMatchObject({ id: '', creating: true, content: '' })
     expect(calls).toHaveLength(0)
   })
 })