feat: make crosswalk and stop-line offsets solvable

Step 1 of the control-marking task, and deliberately server-only: no handle is
drawn yet. This project already shipped a range handle for `profile.interval`,
which compileGeometry ignores, so the control dragged and changed nothing. The
consumer comes first now.

Two kinds join the taxonomy — `junction-crosswalk-inset` and
`junction-stop-line-offset`, both on the existing `junction-approach` anchor. The
solver writes them onto the approach entry, `applyDirectJunctionPlans` carries
them onto the compiled approach, and `compileControlMarkings` reads them in place
of the module constants it used for every junction. They move markings without
reshaping the junction, so unlike width and cutback they deliberately do not
trigger a boundary recompute.

`applyJunctionConstraint` becomes an explicit switch. Its trailing `else` had
meant every kind that was not approach-width fell through to the cutback
validator, so a new kind would have been silently validated and written as a
cutback. The same non-exhaustive shape in the test fixture's `valueFor` is fixed
the same way, and now throws for an unnamed kind rather than answering with a
corner radius.

design.md's taxonomy is updated with it — a test asserts the two cannot drift,
which is what caught the omission.

Measured on a 41-road workspace with 8 crossings: both constraints change their
marking geometry, neither drags the other, and out-of-range blocks instead of
clamping. That measurement is not in the suite: the synthetic junction resolves
`junction_inset_m` to 0 because its crossing never binds to a plan, and the
committed OSM fixture has no crossings at all. The tests assert the wiring the
handles will depend on — values reaching the approach entry, distinct branches,
blocking diagnostics — and the gap is recorded in the test itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.trellis/scripts/common/__init__.py

@@ -0,0 +1,92 @@
+"""
+Common utilities for Trellis workflow scripts.
+
+This module provides shared functionality used by other Trellis scripts.
+"""
+
+import io
+import sys
+
+# =============================================================================
+# Windows Encoding Fix (MUST be at top, before any other output)
+# =============================================================================
+# On Windows, stdout defaults to the system code page (often GBK/CP936).
+# This causes UnicodeEncodeError when printing non-ASCII characters.
+#
+# Any script that imports from common will automatically get this fix.
+# =============================================================================
+
+
+def _configure_stream(stream: object) -> object:
+    """Configure a stream for UTF-8 encoding on Windows."""
+    # Try reconfigure() first (Python 3.7+, more reliable)
+    if hasattr(stream, "reconfigure"):
+        stream.reconfigure(encoding="utf-8", errors="replace")  # type: ignore[union-attr]
+        return stream
+    # Fallback: detach and rewrap with TextIOWrapper
+    elif hasattr(stream, "detach"):
+        return io.TextIOWrapper(
+            stream.detach(),  # type: ignore[union-attr]
+            encoding="utf-8",
+            errors="replace",
+        )
+    return stream
+
+
+if sys.platform == "win32":
+    sys.stdout = _configure_stream(sys.stdout)  # type: ignore[assignment]
+    sys.stderr = _configure_stream(sys.stderr)  # type: ignore[assignment]
+    sys.stdin = _configure_stream(sys.stdin)  # type: ignore[assignment]
+
+
+def configure_encoding() -> None:
+    """
+    Configure stdout/stderr/stdin for UTF-8 encoding on Windows.
+
+    This is automatically called when importing from common,
+    but can be called manually for scripts that don't import common.
+
+    Safe to call multiple times.
+    """
+    global sys
+    if sys.platform == "win32":
+        sys.stdout = _configure_stream(sys.stdout)  # type: ignore[assignment]
+        sys.stderr = _configure_stream(sys.stderr)  # type: ignore[assignment]
+        sys.stdin = _configure_stream(sys.stdin)  # type: ignore[assignment]
+
+
+from .paths import (
+    DIR_WORKFLOW,
+    DIR_WORKSPACE,
+    DIR_TASKS,
+    DIR_ARCHIVE,
+    DIR_SPEC,
+    DIR_SCRIPTS,
+    FILE_DEVELOPER,
+    FILE_CURRENT_TASK,
+    FILE_TASK_JSON,
+    FILE_JOURNAL_PREFIX,
+    get_repo_root,
+    get_developer,
+    check_developer,
+    get_tasks_dir,
+    get_workspace_dir,
+    get_active_journal_file,
+    count_lines,
+    get_current_task,
+    get_current_task_abs,
+    normalize_task_ref,
+    resolve_task_ref,
+    set_current_task,
+    clear_current_task,
+    has_current_task,
+    generate_task_date_prefix,
+)
+
+from .active_task import (
+    ActiveTask,
+    clear_active_task,
+    resolve_active_task,
+    resolve_context_key,
+    set_active_task,
+)