heph.nvim: rip out auto-spawn — connect-only plugin

The daemon is now an OS service (`heph daemon`); the plugin no longer spawns or
supervises one. Removes the managed-daemon machinery entirely.

- delete lua/heph/daemon.lua (spawn/ensure/stop_spawned/self-heal)
- init.lua: connect-only; probe `health` once and guide to `heph daemon start`
- rpc.lua: drop set_respawn + respawn-on-drop; a dropped connection just
  reconnects once (e.g. after `heph daemon restart`), never spawns
- config.lua: drop autostart/bin/db; stable socket fallback (data-dir, matches
  hephd::default_socket_path), keep $HEPH_SOCKET for dev isolation
- tests: spawn/wait_ready move into the e2e harness (test infra); rework
  managed_daemon_spec into a connect-only spec (connect / clean-fail / reconnect)

16 nvim e2e specs pass.

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

heph.nvim/lua/heph/config.lua

@@ -4,15 +4,8 @@ local M = {}
 
 M.defaults = {
   --- Path to hephd's unix socket. `nil` → `$HEPH_SOCKET`, else the daemon default.
+  --- The plugin is connect-only; run the daemon with `heph daemon start`.
   socket = nil,
-  --- DB path for an autostarted local daemon. `nil` → `$HEPH_DB`, else hephd's default.
-  db = nil,
-  --- Plug-and-play: spawn (and manage) a local hephd when none is serving
-  --- `socket`. Set `false` when you run your own daemon (server/client): the
-  --- plugin then connects only, and warns if nothing is reachable.
-  autostart = true,
-  --- hephd binary for autostart (on PATH for an installed heph).
-  bin = "hephd",
   --- Title of the home / index page (`:Heph home`).
   home = "Home",
   --- How many recent days the `:Heph journals` picker offers.
@@ -22,27 +15,24 @@ M.defaults = {
 }
 
 --- Resolve the socket path: explicit opt, then `$HEPH_SOCKET`, then hephd's
---- default (`$XDG_RUNTIME_DIR/heph/hephd.sock`, temp-dir fallback). The env knob
---- lets a dev Neovim target a `mise run dev` daemon without touching real data.
+--- default — `$XDG_RUNTIME_DIR/heph/hephd.sock`, else a **stable**
+--- `<data-dir>/heph/hephd.sock` (matching `hephd::default_socket_path`; not a
+--- temp dir, since the daemon is a persistent service). `$HEPH_SOCKET` lets a
+--- dev Neovim target a `mise run dev` daemon without touching real data.
 function M.resolve_socket(opt)
   opt = (opt and #opt > 0) and opt or vim.env.HEPH_SOCKET
   if opt and #opt > 0 then
     return opt
   end
   local xdg = vim.env.XDG_RUNTIME_DIR
-  local base = (xdg and #xdg > 0) and xdg or (vim.env.TMPDIR or "/tmp")
-  return (base:gsub("/+$", "")) .. "/heph/hephd.sock"
-end
-
---- Resolve the DB path for an autostarted daemon: explicit opt, then `$HEPH_DB`,
---- else nil (let hephd pick its default). Pairs with `resolve_socket` for dev
---- isolation.
-function M.resolve_db(opt)
-  opt = (opt and #opt > 0) and opt or vim.env.HEPH_DB
-  if opt and #opt > 0 then
-    return opt
+  if xdg and #xdg > 0 then
+    return (xdg:gsub("/+$", "")) .. "/heph/hephd.sock"
   end
-  return nil
+  local data = vim.env.XDG_DATA_HOME
+  if not (data and #data > 0) then
+    data = (vim.env.HOME or "") .. "/.local/share"
+  end
+  return (data:gsub("/+$", "")) .. "/heph/hephd.sock"
 end
 
 --- Apply the default keymaps (no-op when `opts.keymaps` is false).