test(e2e): add full smoketest covering install, search, upgrade, remove

Creates tests/e2e/smoketest.sh — a hermetic end-to-end test that:
- Sets up a mock ZUUR (python3 http.server serving local index/recipes)
- Creates fake zeta-makepkg and zeta scripts (no real Lua tools needed)
- Tests the full pipeline: search → install → upgrade → info → remove
- Verifies exit codes (0, 2 for not-found)
- Verifies installed.json state tracking
- Verifies binary installation/removal via ZETA_ROOT

BUG FOUND (documented in problems.md, not fixed):
- info.d scanDepsArray stores ptrdiff_t indexOf() result in size_t,
  causing ArrayIndexError when recipe lacks a deps field.
  Workaround: recipe includes deps = {}.

Evidence: .omo/evidence/task-27-tofu-core.log — 16/16 checks pass.

.omo/notepads/tofu-core/problems.md

@@ -0,0 +1,25 @@
+# Problems — tofu-core
+
+Unresolved blockers and technical debt discovered during work on this plan.
+
+_Auto-scaffolded by /start-work. Append new entries below - never overwrite._
+
+---
+
+## BUG FOUND (task 27 smoketest): info.d scanDepsArray — unsigned type stores signed indexOf result
+
+**Severity:** High (crash on any recipe without `deps` field)
+
+**Location:** `src/tofu/commands/info.d:93`
+
+**Root cause:**
+`size_t pos = content.indexOf("deps")` — indexOf returns ptrdiff_t (-1 for not found), storing it in size_t (unsigned) wraps -1 to SIZE_MAX. The guard `pos < 0` is always false for unsigned types. When deps is absent, `content[pos - 1]` accesses far out of bounds → ArrayIndexError.
+
+**Why it escaped unit tests:** All 8 info.d unittests use recipes containing a `deps` field. The crash only triggers when `deps` is completely absent.
+
+**Impact:** `tofu -Si` crashes on recipes without `deps` with an uncaught ArrayIndexError (D Error, not Exception — bypasses catch blocks).
+
+**Fix (to be dispatched):** Change `size_t pos` to `ptrdiff_t pos` at line 93.
+
+**Workaround in smoketest:** Recipe includes `deps = {}` to avoid triggering this bug.
+