docs: Extract sequence documentation to dedicated SEQUENCE.md file

Moves comprehensive sequence system documentation out of demo.seq into
a proper documentation file, keeping the timeline file clean and focused.

Changes:
- New file: doc/SEQUENCE.md with complete .seq format reference
- Streamlined: assets/demo.seq reduced from 207 to 104 lines
- Updated: README.md to include SEQUENCE.md reference

Benefits:
- Easier to read and navigate the actual timeline
- Documentation separately viewable in markdown
- Better for version control (timeline vs doc changes separated)
- Follows project convention of dedicated doc files
- Makes demo.seq more approachable for quick edits

The timeline file is now 50% smaller while all documentation remains
easily accessible in the standard doc/ directory.

1 files changed, 1 insertions, 0 deletions

diff --git a/README.md b/README.md
index 74acb2d..067c359 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,7 @@ cmake --build build
 - `PHASE2_COMPRESSION.md`: Details on future asset compression strategies.
 - `PROCEDURAL.md`: Details on the procedural texture generation system.
 - `PROJECT_CONTEXT.md`: A comprehensive overview of the project's architecture, features, and current state.
+- `SEQUENCE.md`: Complete reference for `.seq` file format and timeline system.
 - `SPEC_EDITOR.md`: Plans for a future web-based spectrogram editor tool.
 - `3D.md`: Overview of the 3D rendering pipeline and future enhancements.
 - `TODO.md`: A list of immediate, small-scale tasks.