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/workspace/index.md

@@ -0,0 +1,125 @@
+# Workspace Index
+
+> Records of all AI Agent work records across all developers
+
+---
+
+## Overview
+
+This directory tracks records for all developers working with AI Agents on this project.
+
+### File Structure
+
+```
+workspace/
+|-- index.md              # This file - main index
++-- {developer}/          # Per-developer directory
+    |-- index.md          # Personal index with session history
+    |-- tasks/         # Task files
+    |   |-- *.json        # Active tasks
+    |   +-- archive/      # Archived tasks by month
+    +-- journal-N.md     # Journal files (sequential: 1, 2, 3...)
+```
+
+---
+
+## Active Developers
+
+| Developer | Last Active | Sessions | Active File |
+|-----------|-------------|----------|-------------|
+| (none yet) | - | - | - |
+
+---
+
+## Getting Started
+
+### For New Developers
+
+Run the initialization script:
+
+```bash
+python3 ./.trellis/scripts/init_developer.py <your-name>
+```
+
+This will:
+1. Create your identity file (gitignored)
+2. Create your progress directory
+3. Create your personal index
+4. Create initial journal file
+
+### For Returning Developers
+
+1. Get your developer name:
+   ```bash
+   python3 ./.trellis/scripts/get_developer.py
+   ```
+
+2. Read your personal index:
+   ```bash
+   cat .trellis/workspace/$(python3 ./.trellis/scripts/get_developer.py)/index.md
+   ```
+
+---
+
+## Guidelines
+
+### Journal File Rules
+
+- **Max 2000 lines** per journal file
+- When limit is reached, create `journal-{N+1}.md`
+- Update your personal `index.md` when creating new files
+
+### Session Record Format
+
+Each session should include:
+- Summary: One-line description
+- Branch: Which branch the work was done on
+- Main Changes: What was modified
+- Git Commits: Commit hashes and messages
+- Next Steps: What to do next
+
+---
+
+## Session Template
+
+Use this template when recording sessions:
+
+```markdown
+## Session {N}: {Title}
+
+**Date**: YYYY-MM-DD
+**Task**: {task-name}
+**Branch**: `{branch-name}`
+
+### Summary
+
+{One-line summary}
+
+### Main Changes
+
+- {Change 1}
+- {Change 2}
+
+### Git Commits
+
+| Hash | Message |
+|------|---------|
+| `abc1234` | {commit message} |
+
+### Testing
+
+- [OK] {Test result}
+
+### Status
+
+[OK] **Completed** / # **In Progress** / [P] **Blocked**
+
+### Next Steps
+
+- {Next step 1}
+- {Next step 2}
+```
+
+---
+
+**Language**: All documentation must be written in **English**.