feat: /canvas command — visual layer of the wiki

New files:
  commands/canvas.md              — slash command with full trigger table
  skills/canvas/SKILL.md          — complete skill: open, new, add image/text/pdf/note,
                                    zone, list, from-banana operations
  skills/canvas/references/canvas-spec.md — Obsidian canvas JSON spec:
                                    coordinate system, all node types, color table,
                                    image sizing by aspect ratio, auto-positioning
                                    pseudocode, common mistakes, full example

Auto-positioning algorithm (bbox math):
  - Finds rightmost node in target zone
  - Places next node at rightmost_x + 40, same row y
  - If overflow: wraps to new row (max_y_in_zone + 20)
  - Falls back to below all content if no zone found

Banana integration:
  - /canvas from banana: checks .recent-images.txt first, then
    filesystem find -newer 10min, presents list for confirmation
  - After any /banana run: suggests /canvas from banana

Updated:
  skills/wiki/SKILL.md        — added /canvas to routing table
  skills/wiki/references/plugins.md — added Calendar + Thino with
                                      pre-installed note + manual install fallback
  README.md                   — /canvas in commands table + file structure

README.md

@@ -81,6 +81,11 @@ Then scaffold the full wiki structure.
 | `/save` | File the current conversation as a wiki note |
 | `/save [name]` | Save with a specific title (skips the naming question) |
 | `/autoresearch [topic]` | Run the autonomous research loop: search, fetch, synthesize, file |
+| `/canvas` | Open or create the visual canvas, list zones and nodes |
+| `/canvas add image [path]` | Add an image (URL or local path) to the canvas with auto-layout |
+| `/canvas add note [page]` | Pin a wiki page as a card on the canvas |
+| `/canvas zone [name]` | Add a new labeled zone to organize visual content |
+| `/canvas from banana` | Capture recently generated images onto the canvas |
 | `lint the wiki` | Health check: orphans, dead links, gaps, suggestions |
 | `update hot cache` | Refresh hot.md with latest context summary |
 
@@ -198,16 +203,20 @@ cosmic-brain/
 │   ├── wiki-query/              # QUERY operation
 │   ├── wiki-lint/               # LINT operation
 │   ├── save/                    # /save — file conversations to wiki
-│   └── autoresearch/            # /autoresearch — autonomous research loop
+│   ├── autoresearch/            # /autoresearch — autonomous research loop
+│   │   └── references/
+│   │       └── program.md       # configurable research objectives
+│   └── canvas/                  # /canvas — visual layer (images, PDFs, notes)
 │       └── references/
-│           └── program.md       # configurable research objectives
+│           └── canvas-spec.md   # Obsidian canvas JSON format reference
 ├── agents/
 │   ├── wiki-ingest.md           # parallel ingestion agent
 │   └── wiki-lint.md             # health check agent
 ├── commands/
 │   ├── wiki.md                  # /wiki bootstrap command
 │   ├── save.md                  # /save command
-│   └── autoresearch.md          # /autoresearch command
+│   ├── autoresearch.md          # /autoresearch command
+│   └── canvas.md                # /canvas visual layer command
 ├── hooks/
 │   └── hooks.json               # SessionStart + Stop hot cache hooks
 ├── _templates/                  # Obsidian Templater templates