heph.nvim: plug-and-play managed daemon (autostart, self-heal, client/server guardrail)

The plugin now manages its own hephd by default (autostart = true): if nothing
is serving the socket it spawns a local daemon against the default XDG paths,
kills only what it spawned on VimLeavePre, and self-heals — rpc.call retries
once through a respawn hook when the connection drops (the prior owner releases
the DB lock on exit, so a respawn can claim it).

- daemon.ensure() connects to an already-running daemon (any mode) or spawns one
  we own; stop_spawned()/is_managed() track lifecycle.
- A server/client daemon you started is always respected (spawn only when nothing
  serves the socket). autostart = false → connect-only, warns/errors if down,
  and clears the self-heal hook so it fails loudly.
- config: autostart defaults true; new `db` option; $HEPH_SOCKET / $HEPH_DB
  fallbacks isolate a dev Neovim onto a separate daemon + DB.

e2e: managed_daemon_spec covers autostart spawn, self-heal-after-kill, and
connect-only error. 10 specs green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

heph.nvim/plugin/heph.lua

@@ -31,13 +31,16 @@ vim.api.nvim_create_autocmd("BufWriteCmd", {
   end,
 })
 
--- Release the socket cleanly on exit.
+-- Release the socket and stop any daemon this nvim spawned, cleanly, on exit.
 vim.api.nvim_create_autocmd("VimLeavePre", {
   group = grp,
   callback = function()
     pcall(function()
       require("heph.rpc").close()
     end)
+    pcall(function()
+      require("heph.daemon").stop_spawned()
+    end)
   end,
 })