feat(compose): add atelier (bespoke) composition mode + doctrine

Introduce a hand-authored, project-local Remotion render path that bypasses
the cut-schema and the stock scene-type registry, for hero/bespoke videos
that must look distinct from one another.

- video_compose: composition_mode="atelier" (or renderer_family="bespoke")
  routes to _render_via_atelier, which renders a project-local entry under
  remotion-composer/projects/<slug>/ with an optional per-project public_dir
  (skips copying the bloated shared public/). No cut-schema, no stock registry.
- skills/meta/bespoke-composition.md: routing skill — art direction
  (visual-style) -> motion principles (Disney 12) -> engine mechanics
  (remotion-best-practices + stock components read only as a mechanics codex)
  -> atelier render. Doctrine: reuse engine knowledge, never creative components.
- AGENT_GUIDE: "Composition Authoring Mode" (templated vs atelier); default
  atelier for hero work; scene-type catalog reframed as a mechanics codex.
- animation-runtime-selector + INDEX: authoring-mode-first pointers.
- base_tool.run_command: decode subprocess output as UTF-8/replace (Windows
  cp1252 crashed the reader thread on Remotion's Unicode progress output).
- .gitignore: remotion-composer/projects/ (throwaway bespoke compositions).

tools/base_tool.py

@@ -333,6 +333,12 @@ class BaseTool(ABC):
             resolved_cmd,
             capture_output=True,
             text=True,
+            # Force UTF-8 decoding. The default uses the OS locale (cp1252 on
+            # Windows), which raises UnicodeDecodeError on a subprocess that
+            # emits Unicode/emoji (e.g. Remotion's progress output), killing the
+            # reader thread and potentially swallowing the real error text.
+            encoding="utf-8",
+            errors="replace",
             timeout=timeout,
             cwd=cwd,
             check=True,