v0.6.19 — per-edge connection color (hex picker)

v0.6.19 — Per-edge connection color (hex picker)

Each /compose edge can now pick its own color. The Inspector gets a
native color swatch next to the existing label / kind / direction
controls, and the SVG line + arrow head render in the picked color
through the existing currentColor cascade — no new marker shapes.

What you get

• Inspector gets a 4th control: <input type="color"> for the hex
  swatch, plus a small ↺ reset button (visible only when a color is
  set). Click reset to drop the override and fall back to the theme
  accent — same as a v0.6.18 edge.
• Canvas threads the color through style.color on the wrapping
  <g>. The line stroke and the marker fill both consume
  currentColor, so the single style change cascades to both ends.
  Selected vs unselected markers still differ via the existing
  markerId swap; the color is independent of selection state.
• Format is hex-only — #rgb / #rgba / #rrggbb / #rrggbbaa.
  Named colors and rgb() / hsl() are deliberately rejected so the
  "use theme accent" semantic stays clean (a user who wants theme
  default should leave the field empty, not set a color that
  coincidentally matches).

Files touched (15)

Area	Files
Schema	web/src/lib/types.ts, src/core/compose-boards.ts (zod regex + v5 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 (+5 keys)
Docs	CHANGELOG.md, docs/roadmap.md
Tests	2 schema + 4 history + 2 backward-compat (v4↔v5 round-trip)

Backward compat

color is optional in the schema and omitted by default —
same pattern as v0.6.18's dir field. A v0.6.18 board saved before
this release round-trips through v0.6.19 byte-identical (no
color: undefined floating around, no migration script needed).
The schema is now v5; v1 / v2 / v3 / v4 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 is purely additive (every v0.6.18 board still opens
and edits fine), so a minor bump is in line with the project's
release-please conventions.

Backlog after v0.6.19

• v0.6.20 — auto-route (avoid overlapping edges on the canvas)
• v0.6.21 — hooks 抽离 (move web/src/app/api hooks into src/hooks/)
• 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 and the
  schema's color?: string field already supports a future palette
  expansion without a v6 bump.