v0.6.20 — per-edge routing style (curve / orthogonal)

v0.6.20 — Per-edge routing style (curve / orthogonal)

Each /compose edge can now pick between the original cubic bezier
("curve", the v0.6.19 look) and a 3-segment right-angle polyline
("orthogonal", Visio / Lucidchart style). The choice is per-edge,
so a single board can mix both: a "main flow" line curves smoothly
while a "control plane" line goes through right angles.

What you get

• Inspector gets a 5th control: a <select> with the two
  options. The label ("Routing" / "路径") and option labels
  ("Curve" / "曲线" and "Orthogonal" / "直角") are i18n'd.
• Canvas uses a single SVG <path> for both styles. The
  curve case is the original cubic bezier; the orthogonal
  case is a 3-segment polyline (right → up/down → right). Both
  end with a horizontal segment, so the v0.6.18 marker logic
  (markerStart / markerEnd with
  orient="auto-start-reverse") keeps working without any marker
  changes — the orthogonal case's arrow head still sits on the
  last horizontal segment pointing right (or left for backward).

Scope of v0.6.20 (deliberately minimal)

• The two routing styles are the v0.6.20 surface — pick one,
  the renderer takes care of the rest.
• Block-center avoidance is out of scope. A connection that
  goes through other blocks in the middle will still do so with
  "orthogonal". A real A* grid router (or visibility-graph) on
  top of this enum is a separate concern and would need its own
  release. The route field is designed to extend (a future
  obstacleAvoidance?: boolean can layer on top without a v7
  bump).

Files touched (15)

Area	Files
Schema	web/src/lib/types.ts, src/core/compose-boards.ts (zod enum + v6 version union)
Compose state	web/src/lib/compose-history.ts, web/src/app/compose/ComposeBoard.tsx
UI	web/src/app/compose/Inspector.tsx, web/src/app/compose/ConnectionPath.tsx
i18n	web/src/lib/i18n/types.ts, web/src/lib/i18n/dict.en.ts, web/src/lib/i18n/dict.zh.ts (+4 keys)
Docs	CHANGELOG.md, docs/roadmap.md
Tests	3 schema + 4 history + 1 backward-compat (v5↔v6 round-trip)

Backward compat

route is optional in the schema and omitted by default —
same pattern as v0.6.18's dir and v0.6.19's color. A v0.6.19
board saved before this release round-trips through v0.6.20
byte-identical. The schema is now v6; v1 / v2 / v3 / v4 / v5 boards
all continue to load.

Why a minor bump

Same hotfix / additive-feature precedent as v0.6.6, v0.6.13,
v0.6.17, v0.6.18, v0.6.19: v0.6.20 is purely additive (every
v0.6.19 board still opens and edits fine), so a minor bump is in
line with the project's release conventions.

Backlog after v0.6.20

• v0.6.21 — block-center avoidance (real A* grid router on
  top of the v0.6.20 route enum) + hooks 抽离
• placeholder parameter audit (15 keys remain hardcoded)
• per-direction palette (e.g. "all forward connections get this
  color") — deferred; per-edge is the v0.6.19 minimum