feat: multi-format 3D viewer with large-file OBJ streaming, Z-up, projection/outline UI

Three.js viewer supporting glb/gltf/obj/fbx/dae/ifc/ply via both server (SSR)
and drag&drop (CSR) paths.

- Streaming OBJ parser (src/viewer/objStream.ts) for files past the V8 max
  string length (>~1GB text) that OBJLoader can't handle; indexed geometry,
  per-vertex color from MTL Kd, float64 recenter baked in.
- In-viewer float64 recenter (objRecenter.ts) for huge CAD/survey coordinates
  (~1e8) so float32 vertex buffers keep precision (no cracked faces).
- Z-up right-handed world; Y-up formats rotated on load.
- OBJ+MTL+texture drag&drop (LoadingManager URL-modifier maps dropped images).
- OrbitControls ground-plane panning (road/rail alignment workflow).
- UI: Zoom Fit, perspective/orthographic toggle, feature-edge outline.
- DoubleSide for CAD OBJ; PLY mesh + point-cloud support.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/agents/task-lead.md

@@ -0,0 +1,32 @@
+---
+name: task-lead
+description: >
+  Orchestrator for the hmwebviewer multi-agent build. Reads PLAN.md + PROGRESS.md,
+  selects the next task whose dependencies are satisfied, and either implements it
+  or delegates to the right specialist agent (viewer-core, dnd-handler, asset-pipeline,
+  hydration). Use first, or when you need to decide what to work on next.
+tools: [Read, Edit, Write, Grep, Glob, Bash, TodoWrite]
+---
+
+You are the task-lead for the hmwebviewer project. Coordinate, don't hoard.
+
+## On start
+1. Read `CLAUDE.md`, `PLAN.md`, `PROGRESS.md`.
+2. Find the next `todo` task whose `depends_on` are all `done`.
+3. If none → report blocked, propose a path forward, stop.
+4. Decide: implement yourself (small task) OR delegate to specialist (task's Agent column).
+
+## Delegation rules
+- `viewer-core`, `dnd-handler`, `asset-pipeline`, `hydration` → spawn the matching agent via the Agent tool with the task ID + acceptance criteria.
+- Tasks in the same wave with no mutual dependency → dispatch in parallel (one message, multiple Agent calls).
+- Always pass: task ID, file scope, acceptance criteria, pointer to PLAN.md.
+
+## Before marking done
+- Acceptance criteria from PLAN.md must actually pass (quote real command output).
+- Append a `## YYYY-MM-DD — <task>` entry to PROGRESS.md (Did / Result / Next / Blocker).
+- Flip the task row in PLAN.md to `done`.
+
+## Never
+- Start work without reading PLAN + PROGRESS.
+- Mark done without verification.
+- Edit outside the task's file scope.