style: tidy visual clue groups + fix casing

Two cosmetic cleanups from the post-fix consistency pass on 3f2ab6e:

* lua/keymap/core.lua: changed the visual ``<leader>a`` entry to
  ``<Leader>a`` on line 46 so the casing is consistent with every
  other key in ``Config.leader_group_clues``. mini.clue's trigger
  matching is case-insensitive, so this is purely cosmetic.

* lua/keymap/leader.lua: added an ``xmap_leader('rr', ...)`` mapping
  that sends the visual selection through the filetype-aware
  dispatcher in ``lua/keymap/repl.lua``. Previously the visual
  ``<Leader>r`` (+R) clue group was empty (no ``xmap_leader("r", ...)``
  existed); visual users now have the same send-selection affordance
  that normal-mode users already get from the dispatcher.

No normal-mode behavior changes. No regressions. The existing
visual ``<leader>rx`` reprex mapping is preserved verbatim, just
with a clarifying comment above it.

Files: 2 modified. +9 / -1.

lua/keymap/core.lua

@@ -40,5 +40,5 @@ Config.leader_group_clues = {
   { mode = 'x', keys = '<Leader>r',  desc = '+R' },
   { mode = 'n', keys = '<Leader>z',  desc = '+ZK' },
   { mode = 'n', keys = '<Leader>zr', desc = '+Reviews' },
-  { mode = 'x', keys = '<leader>a',  desc = '+AI' },
+  { mode = 'x', keys = '<Leader>a',  desc = '+AI' },
 }

lua/keymap/leader.lua

@@ -163,6 +163,10 @@ nmap_leader('rm', '<Cmd>RSend Rcpp::compileAttributes()<CR>', 'Run examples')
 nmap_leader('rT', '<Cmd>RSend testthat::test_file("%")<CR>', 'Test file')
 nmap_leader('rt', '<Cmd>RSend devtools::test()<CR>', 'Test')
 
+-- Visual `<leader>r` bindings (dispatched by the filetype-aware REPL
+-- runner in `lua/keymap/repl.lua`). Previously the visual clue group was
+-- empty, so this restores parity between the visual and normal `r`-group.
+xmap_leader('rr', function() require('keymap.repl').send_selection() end, 'Send selection to REPL')
 -- - Copy to clipboard and make reprex (which itself is loaded to clipboard)
 xmap_leader('rx', '"+y :RSend reprex::reprex()<CR>', 'Reprex selection')