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/util.lua

@@ -0,0 +1,26 @@
+--- Small shared helpers: URIs, dates, notifications.
+
+local M = {}
+
+--- Today's date as an ISO `YYYY-MM-DD`. Uses the real wall clock — the plugin
+--- picks "today"; `heph-core` stays clock-injected, this is surface-only.
+function M.iso_today()
+  return os.date("%Y-%m-%d")
+end
+
+--- The buffer URI for a node id.
+function M.node_uri(id)
+  return "heph://node/" .. id
+end
+
+--- Parse a `heph://<kind>/<id>` URI into `kind, id` (nil on no match).
+function M.parse_uri(uri)
+  return uri:match("^heph://([^/]+)/(.+)$")
+end
+
+--- Notify with a consistent `heph:` prefix.
+function M.notify(msg, level)
+  vim.notify("heph: " .. msg, level or vim.log.levels.INFO)
+end
+
+return M