chore(#2828): add canary release workflow (#2830)

* chore(#2828): add canary release workflow (dev builds on push to main)

Publishes get-shit-done-cc@canary and @gsd-build/sdk@canary on every
push to main. Version format: {base}-canary.{N} where base strips any
pre-release suffix from package.json (1.39.0-rc.4 → 1.39.0-canary.1).

Sequential canary number is auto-detected from existing git tags so
reruns never collide. Concurrency group cancels stale in-flight canary
runs when commits land quickly.

Mirrors the structure and steps of release.yml: same checkout pins,
Node 24, npm-publish environment, build:sdk, tarball verification,
dry-run publish gate, and publish verification with sleep 10.

Closes #2828

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#2828): address CodeRabbit review findings on canary.yml

- cancel-in-progress: false — was true, allowing a newer push to cancel a
  run mid-publish (after tag push but before SDK publish), leaving a partial
  release state that's unrecoverable since npm versions are immutable

- Guard tag/publish/verify steps with github.ref == 'refs/heads/main' so
  a manual workflow_dispatch from a feature branch (dry_run defaults false)
  cannot accidentally publish unmerged code under the shared canary dist-tag

- Replace fixed sleep 10 with exponential backoff retry loop (delays: 5 10
  20 30 45s); fixed sleep is flaky against normal npm CDN replication lag
  and a false failure forces a new canary number since the tag already exists

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(plan-phase): expose --mvp flag in command frontmatter

Adds --mvp to argument-hint and Flags doc. Workflow handler in next commit.

* chore(#2828): remove push:main trigger from canary workflow

Submission rate to main is too high to auto-publish a canary on every
merge. Restrict the workflow to manual workflow_dispatch only.

Closes #2828

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

commands/gsd/plan-phase.md

@@ -1,7 +1,7 @@
 ---
 name: gsd:plan-phase
 description: Create detailed phase plan (PLAN.md) with verification loop
-argument-hint: "[phase] [--auto] [--research] [--skip-research] [--gaps] [--skip-verify] [--prd <file>] [--reviews] [--text] [--tdd]"
+argument-hint: "[phase] [--auto] [--research] [--skip-research] [--gaps] [--skip-verify] [--prd <file>] [--reviews] [--text] [--tdd] [--mvp]"
 agent: gsd-planner
 allowed-tools:
   - Read
@@ -42,6 +42,7 @@ Phase number: $ARGUMENTS (optional — auto-detects next unplanned phase if omit
 - `--prd <file>` — Use a PRD/acceptance criteria file instead of discuss-phase. Parses requirements into CONTEXT.md automatically. Skips discuss-phase entirely.
 - `--reviews` — Replan incorporating cross-AI review feedback from REVIEWS.md (produced by `/gsd-review`)
 - `--text` — Use plain-text numbered lists instead of TUI menus (required for `/rc` remote sessions)
+- `--mvp` — Vertical MVP mode. Planner organizes tasks as feature slices (UI→API→DB) instead of horizontal layers. On Phase 1 of a new project, also emits `SKELETON.md` (Walking Skeleton). Can be persisted on a phase via `**Mode:** mvp` in ROADMAP.md.
 
 Normalize phase input in step 2 before any directory lookups.
 </context>