feat: copy the output panel to the system clipboard (#11)

New app-level `copy` / `copy all` / `copy last` command (ADR-0041).
Delivery is OSC 52 *and* a best-effort native write (arboard), always
both — OSC 52 acceptance is undetectable, so a true fallback can't be
built. Payload is the panel's plain text exactly as rendered (tags,
✓/✗, box-drawing), drift-locked to render_output_line. arboard added
--no-default-features (X11-only; OSC 52 covers Wayland).

Amends ADR-0003's command registry; requirements V6.

tests/typing_surface/app_commands.rs

@@ -129,6 +129,38 @@ fn messages_with_value_parses() {
     crate::snap!("messages_verbose", a);
 }
 
+#[test]
+fn copy_with_no_value_parses() {
+    // Copy scope is optional — bare `copy` copies the whole panel.
+    let a = assess_at_end("copy", &schema_empty());
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("App(Copy)"));
+    crate::snap!("copy_no_value", a);
+}
+
+#[test]
+fn copy_all_parses() {
+    let a = assess_at_end("copy all", &schema_empty());
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("App(Copy)"));
+    crate::snap!("copy_all", a);
+}
+
+#[test]
+fn copy_last_parses() {
+    let a = assess_at_end("copy last", &schema_empty());
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("App(Copy)"));
+    crate::snap!("copy_last", a);
+}
+
+#[test]
+fn copy_space_offers_all_and_last() {
+    let a = assess_at_end("copy ", &schema_empty());
+    assert_candidate_present(&a, &["all", "last"]);
+    crate::snap!("copy_space", a);
+}
+
 #[test]
 fn partial_entry_word_classifies_as_definite_error_but_completes() {
     // `qu` — mid-typing the `quit` entry word.

tests/typing_surface/mod.rs

@@ -257,6 +257,7 @@ fn command_kind_label(cmd: &rdbms_playground::dsl::Command) -> String {
             AppCommand::Messages { .. } => "App(Messages)".into(),
             AppCommand::Undo => "App(Undo)".into(),
             AppCommand::Redo => "App(Redo)".into(),
+            AppCommand::Copy { .. } => "App(Copy)".into(),
         },
     }
 }

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__app_commands__copy_all_parses@copy_all.snap

@@ -0,0 +1,20 @@
+---
+source: tests/typing_surface/app_commands.rs
+assertion_line: 146
+description: "input=\"copy all\" cursor=8"
+expression: "& a"
+---
+Assessment {
+    input: "copy all",
+    cursor: 8,
+    state: Valid,
+    hint: Some(
+        Prose(
+            "Submit with Enter",
+        ),
+    ),
+    completion: None,
+    parse_result: Ok(
+        "App(Copy)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__app_commands__copy_last_parses@copy_last.snap

@@ -0,0 +1,20 @@
+---
+source: tests/typing_surface/app_commands.rs
+assertion_line: 154
+description: "input=\"copy last\" cursor=9"
+expression: "& a"
+---
+Assessment {
+    input: "copy last",
+    cursor: 9,
+    state: Valid,
+    hint: Some(
+        Prose(
+            "Submit with Enter",
+        ),
+    ),
+    completion: None,
+    parse_result: Ok(
+        "App(Copy)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__app_commands__copy_space_offers_all_and_last@copy_space.snap

@@ -0,0 +1,52 @@
+---
+source: tests/typing_surface/app_commands.rs
+assertion_line: 161
+description: "input=\"copy \" cursor=5"
+expression: "& a"
+---
+Assessment {
+    input: "copy ",
+    cursor: 5,
+    state: Valid,
+    hint: Some(
+        Candidates {
+            items: [
+                Candidate {
+                    text: "all",
+                    kind: Keyword,
+                    mode: Both,
+                },
+                Candidate {
+                    text: "last",
+                    kind: Keyword,
+                    mode: Both,
+                },
+            ],
+            selected: None,
+        },
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                5,
+                5,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "all",
+                    kind: Keyword,
+                    mode: Both,
+                },
+                Candidate {
+                    text: "last",
+                    kind: Keyword,
+                    mode: Both,
+                },
+            ],
+        },
+    ),
+    parse_result: Ok(
+        "App(Copy)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__app_commands__copy_with_no_value_parses@copy_no_value.snap

@@ -0,0 +1,20 @@
+---
+source: tests/typing_surface/app_commands.rs
+assertion_line: 138
+description: "input=\"copy\" cursor=4"
+expression: "& a"
+---
+Assessment {
+    input: "copy",
+    cursor: 4,
+    state: Valid,
+    hint: Some(
+        Prose(
+            "Submit with Enter",
+        ),
+    ),
+    completion: None,
+    parse_result: Ok(
+        "App(Copy)",
+    ),
+}