Phase 0: scaffold tree + manifest

- README, .gitignore, CLAUDE.md (project conventions)
- docs/PHASE0.md — full Phase 0 manifest (locked substrate)
- 10 root .lua modules + 4 ffi/ bindings, all stubs raising NotImplemented
  with module-scoped responsibilities matching the manifest
- config.lua wired to current dirac/hossenfelder endpoints (qwen-coder-7b
  snappy/32k + cloud via OpenRouter through hossenfelder)

File names match docs/PHASE0.md §4 exactly. Module bodies fill in across
later phases; the tree shape is locked.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

executor.lua

@@ -0,0 +1,25 @@
+-- executor.lua — command execution.
+-- Phase 0: io.popen with stderr merge. PTY (forkpty) lands in Phase 1.
+-- `cd` is intercepted before popen and routed through libc chdir so the
+-- working directory persists across calls. See docs/PHASE0.md §7.
+
+local M = {}
+
+-- Execute a shell command.
+-- Returns: (output_string, exit_code).
+function M.exec(cmd)
+    error("executor.exec: not implemented (Phase 0 pending)")
+end
+
+-- Intercept and apply `cd <path>` (or bare `cd` -> $HOME) without forking.
+function M.maybe_chdir(cmd)
+    error("executor.maybe_chdir: not implemented (Phase 0 pending)")
+end
+
+-- Extract `CMD: ...` lines from an assistant response per the broker
+-- contract (PHASE0.md §6 system prompt).
+function M.extract_cmd_lines(text)
+    error("executor.extract_cmd_lines: not implemented (Phase 0 pending)")
+end
+
+return M