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/friendly/strings/en-US.yaml

@@ -224,6 +224,9 @@ help:
         import <zip> [as <t>]    Unpack <zip> into a new project and
                                  switch to it. <t> overrides the target
                                  name (else taken from the zip).
+        copy [all|last]          Copy the output panel to the system
+                                 clipboard (`copy last` copies just the
+                                 most recent command's output).
   # In-app `help` command output (ADR-0024 §help_id). The
   # renderer iterates the command REGISTRY and translates each
   # CommandNode's `help_id` — so a newly-registered command
@@ -266,6 +269,8 @@ help:
         undo                       — undo the last change (with confirmation)
     redo: |-
         redo                       — redo the last undone change (with confirmation)
+    copy: |-
+        copy [all|last]            — copy the output panel to the clipboard (`copy last` = the most recent command)
   ddl:
     create: |-
         create table <T> with pk [<col>(<type>), ...]    — create a table
@@ -563,6 +568,7 @@ parse:
     messages: "messages  |  messages short  |  messages verbose"
     undo: "undo"
     redo: "redo"
+    copy: "copy  |  copy all  |  copy last"
 
 # ---- Pre-submit diagnostics (ADR-0027) -------------------------------
 # Surfaced by the validity indicator and the hint panel before
@@ -852,6 +858,12 @@ messages:
   set_verbose: "messages: verbose"
   unknown: "unknown messages mode '{value}' (expected 'short' or 'verbose')"
 
+# ---- copy (app-level command, ADR-0041) -----------------------------
+copy:
+  done: "copied {count} line(s) to the clipboard"
+  nothing: "nothing to copy — the output panel is empty"
+  unknown: "unknown copy target '{value}' (expected 'all' or 'last')"
+
 # ---- Database-error fallback wording + cascade summaries ------------
 db:
   # DbError variants — fallback Display wording for paths that