heph.nvim: RPC client + buffer editing + wiki-links + journal (slice 11a)

The primary surface begins (tech-spec §8): a Neovim plugin that is a thin
client of the local hephd over its unix-socket JSON-RPC.

- node.resolve {title} → Node|null (heph-core Store + dispatch): exact,
  owner-scoped, non-tombstoned alias-then-title match — the same mapping that
  materializes wiki links, so follow-link jumps to the node the stored link
  points at (never fuzzy search). Unit + rpc_socket integration tests.
- heph.nvim/: vim.uv unix-socket JSON-RPC client (blocking call via vim.wait,
  id-demuxed, partial-line buffered, luanil so JSON null → Lua nil; isolated
  Sessions for tests). Buffer-backed nodes (heph://node/<id>, acwrite;
  BufReadCmd→node.get / BufWriteCmd→node.update, whole-buffer body round-trips
  exactly through the CRDT). [[wiki-link]] follow on <CR>. Daily journal.
  :Heph command surface + completion.
- Headless e2e (§9): a self-contained busted-style runner (tests/e2e/runner.lua)
  — no external plugins, no network, deterministic CI exit codes. Specs: journal
  round-trip, follow-link (+ unresolved no-op), link-two-docs/backlink.
  `make -C heph.nvim test` builds hephd and runs it.

Docs: heph-nvim reference card, §14 tracker (11a done; 11b/11c/11d queued),
changelog fragment.

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

heph.nvim/lua/heph/config.lua

@@ -0,0 +1,39 @@
+--- Configuration defaults, socket resolution, and default keymaps.
+
+local M = {}
+
+M.defaults = {
+  --- Path to hephd's unix socket. `nil` → resolved to the daemon default.
+  socket = nil,
+  --- Spawn a local hephd if the socket is not ready (off by default in v1).
+  autostart = false,
+  --- hephd binary for autostart.
+  bin = "hephd",
+  --- Set the default `<leader>h*` keymaps. `false` to opt out.
+  keymaps = true,
+}
+
+--- Resolve the socket path, mirroring hephd's `default_socket_path`:
+--- `$XDG_RUNTIME_DIR/heph/hephd.sock`, falling back to the temp dir.
+function M.resolve_socket(opt)
+  if opt and #opt > 0 then
+    return opt
+  end
+  local xdg = vim.env.XDG_RUNTIME_DIR
+  local base = (xdg and #xdg > 0) and xdg or (vim.env.TMPDIR or "/tmp")
+  return (base:gsub("/+$", "")) .. "/heph/hephd.sock"
+end
+
+--- Apply the default keymaps (no-op when `opts.keymaps` is false).
+function M.apply_keymaps(opts)
+  if not opts.keymaps then
+    return
+  end
+  local map = vim.keymap.set
+  map("n", "<leader>hj", function()
+    require("heph.journal").open()
+  end, { desc = "heph: today's journal" })
+  -- Task/agenda maps are added with their views in slice 11b.
+end
+
+return M