v1.0.0: merge mouse → input — eliminate cl-tty.mouse package

The mouse-event struct was already in cl-tty.input. All mouse handling
logic (mouse-mixin, hit-test, selection, clipboard, link detection)
was in a separate cl-tty.mouse package. Moved everything into the
input package where the struct lives, eliminating one package boundary.

Changes:
- absorb mouse-mixin, handle-mouse-event, hit-test, selection struct,
  selection variables/functions, cell-link-at, open-link-at into
  text-input.org (tangled to input.lisp)
- update cl-tty.input defpackage with mouse exports
- mouse tests merged into INPUT-SUITE (appended to input-tests.lisp)
- delete mouse.org, mouse-package.lisp, mouse.lisp, mouse-tests.lisp
- update ASDF, run-all-tests.lisp, scripts to drop mouse references

All test suites pass at 100% (INPUT-SUITE: 102 tests, +6 from mouse)

run-all-tests.lisp

@@ -14,7 +14,6 @@
              "tests/scrollbox-tabbar-tests.lisp"
              "tests/markdown-tests.lisp"
              "tests/dialog-tests.lisp"
-             "tests/mouse-tests.lisp"
              "tests/slot-tests.lisp"
              "tests/framebuffer-tests.lisp"
              "tests/integration-tests.lisp"))
@@ -28,8 +27,7 @@
                    (:cl-tty-scrollbox-test "SCROLLBOX-SUITE")
                     (:cl-tty-markdown-test  :cl-tty-markdown-test)
                     (:cl-tty-dialog-test    "DIALOG-SUITE")
-                   (:cl-tty-mouse-test     "MOUSE-SUITE")
-                   (:cl-tty-slot-test      "SLOT-SUITE")
+                    (:cl-tty-slot-test      "SLOT-SUITE")
                    (:cl-tty-layout-test    "LAYOUT-SUITE")
                    (:cl-tty-modern-backend-test "MODERN-BACKEND-SUITE")
                    (:cl-tty-framebuffer-test "FRAMEBUFFER-SUITE")