infra: extract heph.nvim into its own forge repo

The Neovim plugin now lives at eblume/hephaestus.nvim (plugin at the repo
root). Remove heph.nvim/ from the monorepo and the build/test wiring that
referenced it:

- Dagger: drop the test_nvim function + the pinned-Neovim NVIM_VERSION
- build.yaml: drop the `dagger call test-nvim` step
- drop the mise run test-nvim task and .stylua.toml + the stylua prek hook
  (no Lua remains in the monorepo)
- install-heph.md: install via a plain lazy.nvim spec pointing at the
  plugin repo over SSH (no more local-dir checkout hack)
- README / AGENTS / heph-nvim.md: note the surface lives in its own repo

The CLI/TUI -> nvim integration is unchanged (they shell out to `nvim`
expecting the heph plugin installed). The v1-prototype tech-spec §14 build
record and prior changelog fragments are left as frozen history.

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

docs/changelog.d/extract-heph-nvim.infra.md

@@ -0,0 +1 @@
+Extracted the Neovim plugin into its own forge repo, [eblume/hephaestus.nvim](ssh://forgejo@forge.ops.eblu.me:2222/eblume/hephaestus.nvim.git). Removed `heph.nvim/` from the monorepo along with its build/test wiring: the `test_nvim` Dagger function, the `dagger call test-nvim` CI step, the `mise run test-nvim` task, and the `.stylua.toml` + stylua prek hook (no Lua remains here). The CLI/TUI→nvim integration is unchanged (they shell out to `nvim` expecting the plugin installed). Install now uses a plain lazy.nvim spec pointing at the plugin repo — see [[install-heph]].

docs/how-to/install-heph.md

@@ -33,20 +33,15 @@ real data.
 
 ## 2. The Neovim plugin
 
-`heph.nvim` lives in a subdirectory of the monorepo, and lazy.nvim can't load a
-subdir plugin from a bare git URL (it puts the clone *root* on `runtimepath`).
-For now, point lazy at a dedicated checkout via `dir`:
-
-```bash
-git clone --branch feature/v1-prototype \
-  ssh://forgejo@forge.ops.eblu.me:2222/eblume/hephaestus.git \
-  ~/.local/share/heph/checkout
-```
+The plugin lives in its own forge repo,
+[eblume/hephaestus.nvim](ssh://forgejo@forge.ops.eblu.me:2222/eblume/hephaestus.nvim.git),
+with the plugin at the repo root — so lazy.nvim loads it from a bare git URL.
+Point lazy at the forge over SSH:
 
 ```lua
 -- lazy.nvim spec
 {
-  dir = vim.fn.expand("~/.local/share/heph/checkout/heph.nvim"),
+  url = "ssh://forgejo@forge.ops.eblu.me:2222/eblume/hephaestus.nvim.git",
   config = function()
     require("heph").setup({}) -- connect-only: talks to the daemon you started
   end,
@@ -61,9 +56,8 @@ heph daemon start    # launchd agent (macOS) / systemd user service (Linux)
 ```
 
 See [[run-the-daemon]] for `start`/`stop`/`restart`/`status`. Update the plugin
-by `git pull`ing the checkout (and after a `cargo install` upgrade, `heph daemon
-restart` to pick up the new `hephd`). (A future split of `heph.nvim` into its own
-forge repo will make this a normal `{ "eblume/heph.nvim" }` spec.)
+with `:Lazy update` (and after a `cargo install` upgrade of the binaries, `heph
+daemon restart` to pick up the new `hephd`).
 
 ## 3. Isolate development
 

docs/reference/heph-nvim.md

@@ -8,15 +8,20 @@ tags:
 
 # heph.nvim
 
-The primary user surface (tech-spec §8): a Neovim plugin that replaces
+The Neovim knowledge-base surface (tech-spec §8): a plugin that replaces
 obsidian.nvim and is a **thin client of the local `hephd`** over its
 unix-socket JSON-RPC. Notes, journals, and tasks are edited as ordinary
-buffers; the daemon owns all storage and sync. Built in checkpointed slices on
-`feature/v1-prototype`; this card tracks the stable surface as it lands.
+buffers; the daemon owns all storage and sync.
+
+> **Repo:** the plugin code lives in its own forge repo,
+> [eblume/hephaestus.nvim](ssh://forgejo@forge.ops.eblu.me:2222/eblume/hephaestus.nvim.git)
+> (extracted from this monorepo). This card documents the surface's
+> architecture; see [[install-heph]] to install it and the plugin repo for the
+> Lua sources + headless e2e suite.
 
 ## Architecture
 
-`heph.nvim/lua/heph/` modules, each small and single-purpose:
+The `lua/heph/` modules, each small and single-purpose:
 
 | Module | Responsibility |
 |---|---|
@@ -109,13 +114,11 @@ The headless e2e suite drives the plugin in `nvim --headless` against a real
 `hephd` over a temp socket, asserting both buffer contents and resulting DB
 state (via an isolated RPC session). It uses a **self-contained busted-style
 runner** (`tests/e2e/runner.lua`) — no external plugins, no network — so it is
-deterministic. `mise run test-nvim` builds the daemon and runs the suite against
-system-installed Neovim; a deliberately failing spec exits non-zero (no
-false-green; the runner also fails if it discovers zero specs). CI runs the same
-suite through the **`test-nvim` Dagger function** (`.dagger/`, invoked by
-`build.yaml` as `dagger call test-nvim`), which bakes a pinned, arch-detected
-Neovim onto a Rust image, builds `hephd`, and runs the suite — reproducible, and
-identical to the native `mise run test-nvim` path.
+deterministic. The suite lives in the plugin repo (eblume/hephaestus.nvim); since
+that repo carries no Rust source, `mise run test-nvim` there drives the suite
+against a prebuilt `hephd` supplied via `$HEPHD_BIN` (built from this monorepo:
+`cargo build -p hephd`). A deliberately failing spec exits non-zero, and the
+runner also fails if it discovers zero specs — no false-green.
 
 ## Related