docs: add project context and ubiquitous language

CONTEXT.md

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+# Dantotsu Print
+
+Tooling that moves code-quality defects from the IDE onto the physical
+"Daily — Dantotsu and Problem Solving" board with minimal friction, preserving
+the Dantotsu ritual of *visualizing the defect* — which for developers means
+seeing the actual lines of code.
+
+## Language
+
+**Board**:
+A **magnetic whiteboard** displaying one or more **A3 sheets** held by magnets, refreshed on a **daily** cadence.
+_Avoid_: Notion database — the low-friction digital habit this tool exists to displace.
+
+**A3 sheet**:
+The printed "Daily — Dantotsu and Problem Solving" 5-column template, magnet-mounted on the Board, one row per defect.
+
+**Defect card**:
+The printed **monochrome peel-and-stick label** bearing the defective code + `path·lines·@sha` footer (+ optional QR), stuck into the **Defect** cell of an A3 sheet — the physical "photo of the defect."
+
+**Defect** (the printed artifact; column 2 of the board):
+A code-quality defect — the defective lines of code are themselves the nonconformance (e.g. a switch missing a case). This is what gets printed and placed in the **Defect** cell: the "photo of the defect," the *before* state.
+_Avoid_: "Problem" for the artifact — the board column is labeled **Defect**. Never use it to mean the user-visible symptom (the crash), which is only the consequence that made the defect visible.
+
+**Occurrence cause**:
+Why the defect was introduced. (Handwritten, Causes column.)
+
+**Late detection cause**:
+Why the defect was not caught earlier. (Handwritten, Causes column.) — the Toyota dual-cause split.
+
+**Countermeasure**:
+The fix plus the process change that prevents recurrence. (Handwritten.)
+
+**Status quadrant**:
+The 4-step visual progress marker on each row: 1) Defect identified → 2) Cause found → 3) Countermeasure done → 4) Defect eradicated or **yokoten** (horizontally deployed).
+
+## Board columns (left → right)
+
+Date | **Defect** | Causes (Occurrence / Late detection) | Counter measures | Resp. person | Status
+
+## Division of labor
+
+- **Machine prints** only the **Defect** cell: defective code snippet + file/line + commit SHA + QR permalink.
+- **Human handwrites** everything else: date, causes, countermeasures, responsible person, status.
+
+## Relationships
+
+- A **Board** holds many **Defects**, one per row.
+- A **Defect** is visualized by a printed snippet of the defective code placed in the Defect cell.
+
+## Flagged ambiguities
+
+- "problem" vs "defect": the board column is literally **Defect**. **Resolved:** *Defect* is canonical for the printed artifact; "Problem solving" names the overall ritual/board, not the artifact.
+- "problem" was also used to mean the consequence (app crash). **Resolved:** the crash is the consequence, not the defect; it is not printed.