feat(dev-env): backport matured dev-env implementation from /etc/nixos

Replace the stub dev-env with the real, working implementation that grew
in the reference machine config — de-identified for the public scaffold.

Nix layer:
- options.nix: full project schema (url/upstream/fork/category/
  worktreeRoot/worktrees{branch,path,remote}/isClone/deployFlakeInput),
  deploy.targets, github.forkUser, writeDirenvHints. Drops the
  forgejo-URL block + deploy-flake auto-derivation (incoherent in a
  scaffold that uses explicit per-project urls).
- lib.nix: mkProject + worktreePath/bareRepoPath/projectRemotes,
  generalized to the explicit-url model (origin falls back to upstream).
- config.nix: renders /etc/dev-env/{config.sh,projects.json,
  tmux-sessions.json}, installs helpers via writeShellScriptBin, loads
  shell functions into interactive shells, wires the git pre-commit hook.

Scripts (config-driven, read /etc/dev-env at runtime):
- bootstrap.sh, nav.sh, worktree.sh, pr-helpers.sh, rebase.sh,
  status.sh, deploy.sh, regtest.sh, tmux-launch.sh.
- Stripped aiolabs/forgejo/bitspire/lamassu/webapp hardcoding; the
  github-fork remote is renamed 'fork' to match git.remotes vocabulary.
- Removes the dev.sh stub (the matured impl uses discrete commands +
  shell functions, not a unified 'dev' CLI).

presets/example.nix: a worked, generic project list replacing the
identity-specific aiolabs preset. tests/smoke.nix + flake checks
exercise the schema; 'nix flake check' is green.

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

modules/dev-env/presets/example.nix

@@ -0,0 +1,104 @@
+# Example dev-env preset — a worked, generic project list.
+#
+# Importing this file is opt-in and illustrative. Copy it, rename it,
+# and edit the URLs / worktrees / targets for your own stack. The
+# dev-env module ships **no** projects by default — you declare them
+# either here or inline in your host config.
+#
+# Wire it up in configuration.nix:
+#
+#   imports = [
+#     ./modules/dev-env
+#     ./modules/dev-env/presets/example.nix
+#   ];
+#
+# Then `nixos-rebuild switch` and `dev-env-bootstrap` to materialize the
+# bare repos + worktrees on disk.
+{ config, lib, ... }:
+
+let
+  # `mk` cuts boilerplate: derives the `fork` remote from
+  # github.forkUser, defaults worktreeRoot to the project name, etc.
+  mk = config.lnbits-sensei.devEnv.lib.mkProject;
+in
+{
+  lnbits-sensei.devEnv = {
+    # Personal github username — used to derive `fork` remotes for any
+    # project that declares an upstream. Leave null if you never send
+    # upstream PRs.
+    github.forkUser = lib.mkDefault "octocat";
+
+    # Hostname → SSH target map for `dev-deploy`. Empty by default.
+    deploy.targets = lib.mkDefault {
+      # prod    = "root@prod-host";
+      # staging = "root@staging-host";
+    };
+
+    projects = {
+
+      # ─── lnbits: your fork, dev + main worktrees tracking upstream ──
+      #
+      # `url` is your origin (your fork on whatever git host you use).
+      # `upstream` adds the lnbits/lnbits remote so the rebase + sync
+      # helpers (lnbits-status, lnbits-sync-dev, rebase) work.
+      lnbits = mk {
+        name = "lnbits";
+        url = "git@github.com:octocat/lnbits.git";
+        upstream = "https://github.com/lnbits/lnbits";
+        deployFlakeInput = "lnbits";
+        worktrees = {
+          dev.branch = "dev";
+          main.branch = "main";
+        };
+      };
+
+      # ─── an LNbits extension, grouped under an `extensions` category ─
+      #
+      # Single clone (one branch checked out at a time). Lands at
+      # ${root}/extensions/myext.
+      myext = mk {
+        name = "myext";
+        category = "extensions";
+        url = "git@github.com:octocat/myext.git";
+        upstream = "https://github.com/lnbits/myext";
+        isClone = true;
+      };
+
+      # ─── a pure-upstream reference checkout (no fork, read-only) ─────
+      #
+      # No `url` → origin falls back to `upstream`. Useful for grepping
+      # a reference codebase alongside your own work.
+      nostr-tools = mk {
+        name = "nostr-tools";
+        category = "refs";
+        upstream = "https://github.com/nbd-wtf/nostr-tools";
+        worktrees.master.branch = "master";
+      };
+    };
+
+    # ─── a declarative tmux session for the lnbits dev loop ───────────
+    tmux = {
+      enable = lib.mkDefault true;
+      sessions.lnbits = {
+        cwd = "lnbits/dev";
+        windows = [
+          {
+            name = "edit";
+            cwd = "lnbits/dev";
+            cmd = "nvim .";
+          }
+          {
+            name = "run";
+            cwd = "lnbits/dev";
+            cmd = null;
+          }
+          {
+            name = "git";
+            cwd = "lnbits/dev";
+            cmd = "lazygit";
+          }
+        ];
+      };
+    };
+  };
+}