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.

src/dsl/grammar/app.rs

@@ -7,7 +7,7 @@
 //! builder, help / usage references. The ast_builders match
 //! against the `MatchedPath` items in declaration order.
 
-use crate::dsl::command::{AppCommand, Command, MessagesValue, ModeValue};
+use crate::dsl::command::{AppCommand, Command, CopyScope, MessagesValue, ModeValue};
 use crate::dsl::grammar::{
     CommandNode, HintMode, IdentSource, IdentValidator, Node, ValidationError,
     Word,
@@ -37,8 +37,16 @@ fn validate_unknown_messages(value: &str) -> Result<(), ValidationError> {
     })
 }
 
+fn validate_unknown_copy(value: &str) -> Result<(), ValidationError> {
+    Err(ValidationError {
+        message_key: "copy.unknown",
+        args: vec![("value", value.to_string())],
+    })
+}
+
 const UNKNOWN_MODE_VALIDATOR: IdentValidator = validate_unknown_mode;
 const UNKNOWN_MESSAGES_VALIDATOR: IdentValidator = validate_unknown_messages;
+const UNKNOWN_COPY_VALIDATOR: IdentValidator = validate_unknown_copy;
 
 // --- Shapes (constants are referenced by Optional/Choice slices) --
 
@@ -114,6 +122,29 @@ const MESSAGES_CHOICES: &[Node] = &[
 const MESSAGES_VALUE: Node = Node::Choice(MESSAGES_CHOICES);
 const MESSAGES_VALUE_OPT: Node = Node::Optional(&MESSAGES_VALUE);
 
+// `copy [all|last]`: same shape as `messages` — known scope words are
+// `Word` siblings (so they reach completion + the expected set); the
+// trailing catch-all `Ident` funnels any other word into the friendly
+// `copy.unknown` validator. Bare `copy` (no value) means `all`.
+const COPY_CHOICES: &[Node] = &[
+    Node::Word(Word::keyword("all")),
+    Node::Word(Word::keyword("last")),
+    Node::Ident {
+        source: IdentSource::Free,
+        role: "copy_value",
+        validator: Some(UNKNOWN_COPY_VALIDATOR),
+        highlight_override: None,
+        writes_table: false,
+        writes_column: false,
+        writes_user_listed_column: false,
+        writes_table_alias: false,
+        writes_cte_name: false,
+        writes_projection_alias: false,
+    },
+];
+const COPY_VALUE: Node = Node::Choice(COPY_CHOICES);
+const COPY_VALUE_OPT: Node = Node::Optional(&COPY_VALUE);
+
 const EMPTY_SEQ: Node = Node::Seq(&[]);
 const SAVE_AS_OPT: Node = Node::Optional(&SAVE_AS_WORD);
 
@@ -202,6 +233,17 @@ fn build_messages(path: &MatchedPath, _source: &str) -> Result<Command, Validati
     Ok(Command::App(AppCommand::Messages { value }))
 }
 
+fn build_copy(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
+    // The unknown-value branch's validator always errors, so reaching
+    // here means either a known scope word or a bare `copy` (= all).
+    let scope = if path.contains_word("last") {
+        CopyScope::Last
+    } else {
+        CopyScope::All
+    };
+    Ok(Command::App(AppCommand::Copy { scope }))
+}
+
 // --- Command nodes -------------------------------------------------
 
 pub static QUIT: CommandNode = CommandNode {
@@ -287,3 +329,10 @@ pub static REDO: CommandNode = CommandNode {
     ast_builder: build_redo,
     help_id: Some("app.redo"),
     usage_ids: &["parse.usage.redo"],};
+
+pub static COPY: CommandNode = CommandNode {
+    entry: Word::keyword("copy"),
+    shape: COPY_VALUE_OPT,
+    ast_builder: build_copy,
+    help_id: Some("app.copy"),
+    usage_ids: &["parse.usage.copy"],};

src/dsl/grammar/mod.rs

@@ -613,6 +613,7 @@ pub static REGISTRY: &[(&CommandNode, CommandCategory)] = &[
     (&app::MESSAGES, CommandCategory::Simple),
     (&app::UNDO, CommandCategory::Simple),
     (&app::REDO, CommandCategory::Simple),
+    (&app::COPY, CommandCategory::Simple),
     (&ddl::DROP, CommandCategory::Simple),
     (&ddl::ADD, CommandCategory::Simple),
     (&ddl::RENAME, CommandCategory::Simple),