Add archify skill (v2.14), pi-mermaid ext (v0.3.0), project-diagramming-mermaid + project-diagramming-archify skills

- skills/archify: vendored tt-a1i/archify 2.14.0 (MIT), pure Node 18+, zero deps
- extensions/pi-mermaid: renders mermaid blocks as ASCII in TUI; deps beautiful-mermaid + mermaid
- skills/project-diagramming-*: orchestration skills, per-project docs/ convention

skills/archify/renderers/workflow/README.md

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+# Workflow Renderer
+
+Render `diagram_type: "workflow"` JSON files into the standard Archify HTML
+template.
+
+```bash
+node archify/renderers/workflow/render-workflow.mjs input.workflow.json output.html
+```
+
+The renderer validates input against `archify/schemas/workflow.schema.json`
+with the bundled standalone validator. No dependency installation is required.
+
+If `output.html` is omitted, the renderer uses `meta.output` from the JSON file
+or falls back to `workflow.html` in the current working directory.
+
+After rendering, run the artifact checker:
+
+```bash
+node archify/scripts/check-render-output.mjs output.html
+```
+
+It catches final-SVG issues that are easiest to see in a browser: non-finite
+SVG values, accidental two-point diagonal arrows, and arrows crossing the
+legend.
+
+## Input
+
+Workflow JSON files must set:
+
+```json
+{
+  "schema_version": 1,
+  "diagram_type": "workflow",
+  "meta": {
+    "title": "Agent Tool Call Workflow"
+  },
+  "lanes": [],
+  "phases": [],
+  "groups": [],
+  "mainPath": [],
+  "nodes": [],
+  "edges": [],
+  "cards": []
+}
+```
+
+Omit `meta.viewBox` for the common case: the width is fixed at 720 and the
+height is derived from the lane count, so lanes and legend always fit. A
+complete worked example lives at
+`archify/examples/agent-tool-call.workflow.json`.
+
+The schema lives at:
+
+```text
+archify/schemas/workflow.schema.json
+```
+
+## Legend
+
+The default legend derives component kinds from `nodes[].type`. Supported
+`meta.legend.entries` keys, in stable order, are `frontend`, `backend`,
+`security`, `messagebus`, `database`, `cloud`, and `external`. Labels and
+visibility may be overridden through the shared legend contract; only kinds
+backed by rendered nodes receive Semantic Legend controls.
+
+## Layout budget
+
+| Constant | Value |
+|----------|-------|
+| viewBox | default `[720, auto]` — auto height = 52 + lanes×104 + (lanes−1)×20 + 124 |
+| Lane frame | x 40, width 640, height 104, gap 20; first lane top at y 52 |
+| Lane title strip | top 30px of each lane; node boxes must stay below it |
+| Column centers (`col` 0–5) | x = 88, 220, 300, 430, 500, 625 |
+| Phase headers | Optional `phases[]` render above the first lane, spanning `fromCol..toCol` |
+| Lane groups | Optional `groups[]` frame parallel work or branch work inside one lane |
+| Exception lanes | Set `lane.variant: "exception"` for retry, denial, fallback, or failure paths |
+| Main path lint | Optional `mainPath[]` checks that happy-path steps have matching edges and do not move backward |
+| Default node | 92×52 (height 68 when `tag` is set) |
+| Node spacing | ≥8px between nodes in the same lane |
+| Edge length | straight segments must span ≥28px |
+| Legend row | y = lane bottom + 44; viewBox height must be ≥ legend y + 18 |
+
+Column-center gaps are 132 / 80 / 130 / 70 / 125 px: columns 1↔2 (80px) and
+3↔4 (70px) cannot both hold default-width 92px nodes in the same lane — skip a
+column or reduce `width`.
+
+## Design Rules
+
+- Use lanes for ownership or runtime boundaries.
+- Use phase headers for high-level story beats such as Intake, Plan, Execute, and Report.
+- Use groups for parallel checks, branch handling, or bounded work within a lane; every group must contain at least one node.
+- Use `lane.variant: "exception"` for human wait, denial, retry, fallback, and failure lanes instead of mixing those paths into the happy path.
+- Set `mainPath` when the diagram has a clear happy path; the renderer validates that consecutive ids have matching edges and move left-to-right.
+- Place nodes with lane IDs and column indexes, not raw SVG coordinates.
+- Leave short adjacent links unlabeled; the arrow is enough.
+- Use labels for cross-lane decisions, approvals, async traces, and return paths.
+- Prefer route presets — `drop` (bend between lanes; `bias` 0–1 picks where),
+  `outside-right`, `return-left`, `bottom-channel`, and `up-channel` — before
+  using raw `via` points. `straight` and the default `auto` cover the rest.
+- Keep workflow examples compact enough to render well in narrow chat/browser
+  previews.
+
+Schema violations exit non-zero with path-prefixed messages annotated with the
+element's id or label. The renderer additionally fails when it can detect
+layout problems, including node overlap, nodes outside their lanes, invalid
+phase/group column ranges, empty groups, broken `mainPath` steps, unknown edge
+targets, labels colliding with nodes or other labels, labels wider than their
+node, legends outside the viewBox, or straight arrows that are too short to
+read cleanly. The shared Clean Flow Gate also rejects edges crossing unrelated
+nodes with 2px clearance; lanes, phases, and groups remain intentional
+pass-through containers. Text width is estimated CJK-aware: fullwidth glyphs
+count as two units.
+
+Set `meta.quality_profile` to `showcase` for polished delivery. Unrelated proper
+X crossings then fail with `composition/proper-crossing`; default `standard`
+keeps them as artifact-receipt warnings. Collinear lane corridors are outside
+the proper-X rule, but a separate gate warns in `standard` and fails in
+`showcase` when unrelated edges overlap for at least 8px. Shared semantic
+endpoints, point touches, and shorter overlaps remain valid. Showcase also
+rejects any route segment below 8px and any interior turn segment below 16px;
+ordinary 8–15px endpoint stubs remain valid for fixed lane gaps.