v0.4.0 — DisC Studio launch

The wizard grew up. It's now DisC Studio — the companion editor for
DisC. Designs are first-class authoring objects with decision tables,
explicit system-under-test marking, and a step composer you can actually
live in: one-line rows, click-to-edit pills, insert-anywhere wedges,
duplicate, hover-only delete, drag-reorder with a visible grip. Two demo
seeds (a 4-participant loop example and the full 10-participant order
flow) cover both ends of the complexity gradient.

Added

• Decision tables, first-class. Any CALL step can be marked
  decision-table-backed via a + DT chip on the step row. Click opens a
  modal editor with the method signature as a read-only header, a config
  form (nullHandling, exceptionType/defaultValue, rounding,
  scale, locale — the keys java_spring.md enumerates), and a
  freeform rows table. "Save to project" writes the .puml plus one
  <Participant>.decision.md sidecar per DT-backed call into the same
  design/ folder.
• System-under-test mark + entry interaction. Each participant card
  shows a + SUT chip. Marking auto-adds the entry interaction
  ([*] -> SUT : method(...)) and final return ([*] <-- SUT : Type).
  Single-method SUTs get the boundary steps instantly; multi-method SUTs
  prompt via an inline "pick entry method" banner on Step 2. Required
  for DisC v0.5.x — Step 1 refuses any .puml without exactly one
  system_caller.
• Step composer overhaul for read, write, and modify:
  • Each CALL renders on one line instead of two — the trailing
    return type is a muted inline suffix, halving vertical space. The
    13-step complex demo fits on a single screen.
  • Caller, callee, and method are click-to-edit pills. Click opens
    a small popover scoped to valid choices; Esc / outside-click
    dismisses. Method-edit is one click, not "delete + re-pick three
    dropdowns."
  • Insert-anywhere wedges between adjacent rows. Hover the gap
    between steps, click + insert here, the composer relocates inline.
  • Per-row duplicate (⎘) button deep-copies the step including any
    attached decision table. Delete (×) and duplicate now hover-only to
    reduce idle noise.
  • Visible 6-dot grip glyph advertises the drag-reorder affordance
    that was already there but invisible.
  • Composer's caller dropdown prefills from the last CALL's caller
    (the common "same orchestrator throughout" case).
• Two demo seeds, side by side. "Load simple demo" seeds a
  4-participant loop example (matches the 03_loop.puml corpus).
  "Load complex demo" seeds the 10-participant order flow with three
  pre-populated decision tables (matches 06_order/PlaceOrder.puml).
  First-timers can climb from one to the other.
• Target-package autocomplete on Step 4. Suggestions come from the
  unique packageNames in the scanned project. Free typing still works.
  The list is persisted to localStorage so it survives a page reload
  before reconnecting.
• Plugin pre-flight gets an Update flow. When the installed
  design-is-code plugin is older than the latest GitHub release, an
  "Update plugin" banner appears next to "Run it for me" with the new
  version + changelog link + a one-click installer. Skip-for-session
  also available.
• Boundary box auto-fit. Participant boxes in the live SVG measure
  their rendered text width (getBBox()) instead of guessing 8px/char,
  so long names like LineSubtotalCalculator never clip.

Changed

• Renamed to "DisC Studio" (user-facing). <title>, <h1>,
  README all reframed: DisC owns codegen; the Studio owns design
  authoring. The Java package, Gradle artifact name, plugin slug, and
  repo URL are unchanged — this is a Tier-1 brand rename.
• PlantUML emitter uses the SUT-anchored arrow style from the
  canonical .puml corpus: returns emit <-- (dashed) instead of
  <- (solid), and the boundary marker [*] always anchors the left
  side of every line — both for entry ([*] -> SUT) and final return
  ([*] <-- SUT). Visually distinguishes returns from forward calls.
• DisC step-name display synced to the v0.5.1 SKILL: Validate Inputs → Validate Design, Classify → Classify Participants,
  Discover Context → Resolve Targets, Generate → Generate Tests, Quality Gate → Check Tests, Implement → Generate Implementation. Step numbers unchanged. The run-event regex is
  number-only so live event mapping was unaffected; this is display
  only.
• Participant cards drop the noisy CALLER/IMPL header badges —
  premature surface for half-shipped affordances. Grid minmax raised
  from 13rem to 18rem so cards have room for typical method signatures;
  method line wraps within the card instead of ellipsizing.
• Plugin-update flash simplified. The post-update pill no longer
  says "restart Claude Code" (nothing needs restarting — each "Run it
  for me" spawns a fresh claude process that picks up the new
  plugin). Reads DisC plugin updated to v<X> ✓ then settles to the
  normal status pill.
• Story textarea placeholder changed from a concrete example to
  the canonical three-part template As a <role>, I want to <action>, so that <outcome>. Teaches the shape, not just the tone.
• Step 2 terminology cleanup: + new class → + new participant;
  N classes counter → N participants. Matches the participant data
  model.
• Modal copy: "generate a stub class alongside the interface" →
  "also generate the implementation class alongside the interface."
  Stub was misleading — DisC emits a real implementation.

Breaking

• Hand-built designs need a SUT. DisC v0.5.x refuses any .puml
  without exactly one system_caller. Loading either demo handles
  this automatically. For hand-built designs, click + SUT on the
  participant that is your entry point — Studio adds the boundary
  steps for you. Pre-v0.4.0 designs saved before this release will
  need the SUT marked before they can be re-run.
• The CALLER and IMPL badges on participant cards are gone. No
  behavior change beyond visual — the underlying implByDefault flag
  is still stored on each participant.