refactor(tooling): T-1286 — generate, pr and dev become reach domains

Twelve scripts retired, three domains registered. `reach` now covers nine.

generate: `generate-brands` and `generate-corporations` were the second and
third copies of the same 24-line build-if-missing-then-exec bash `tooling/atlas`
carried, so they collapsed into `core.process.cargo_binary` rather than being
ported. `import_economics` shelled out to the first of those, so it now calls
that helper — `generated_brands.toml` comes back byte-identical, and the stamp
registry swaps the retired wrapper for `core/process.py`.

pr: `watchlist-diff` derives its watched set from `generator_sources.py` instead
of restating it, so it cannot drift from the stamp check.

dev: the environment scripts split decision from performing, per D-263's
guarded-exec rule. `godot_plan()` and `worktree_plan()` decide what would
happen; `install_godot()`, `install_rust()` and `setup_worktree()` do it.
`tooling/test_environment.py` pins the version pin, both override precedences,
the already-current skip, the platform refusal and both worktree refusals —
none of them performed. `make setup` now installs reach first, since the
targets that install rust and godot are reach verbs.

Two live bugs found while porting:

- The clerk read its decision index from `decisions/README.md`, a path that
  stopped existing when the DQR tree moved to `governance/`. Every clerk agent
  has been grepping blind; its prompt pointed at the same dead directory.
- The conformance exec-check matched any `x.system()` regardless of receiver,
  so `platform.system()` read as `os.system()`. Narrowed and re-proved against
  a real mutant.

`process.run` gains `input=`, `timeout=` and a `ProcessTimeout` subclass so a
killed run stays distinguishable from a verdict. The pre-push hook no longer
merges the clerk's stderr into its stdout — under streaming the last merged
line is a JSONL event, which would read as an unrecognised verdict and block.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tooling/test_conformance.py

@@ -167,9 +167,14 @@ def check_one_guarded_exec(failures: list[str]) -> None:
                 "missing-binary message and the failure remedy live"
             )
         for node in ast.walk(tree):
+            # The receiver has to be checked, not just the attribute name:
+            # `platform.system()` is a legitimate call and shares a name with
+            # `os.system()`. A check that fires on the wrong thing gets muted.
             if (
                 isinstance(node, ast.Call)
                 and isinstance(node.func, ast.Attribute)
+                and isinstance(node.func.value, ast.Name)
+                and node.func.value.id == "os"
                 and node.func.attr in {"system", "popen", "execv", "execvp"}
             ):
                 failures.append(