feat(marketing/channels): Dev.to adapter

[blove]

Summary

Follow-up to PR #425 (X channel adapter). Implements the Dev.to adapter behind the same ChannelAdapter interface.

Changes:

• Extends Draft with optional article: DraftArticle (title, tags, canonicalUrl, description). Future LinkedIn long-form posts will reuse this shape.
• New DevToAdapter class: single API key auth (DEVTO_API_KEY), single POST endpoint, real metrics() (Dev.to's read API is free).
• post() publishes immediately (published: true) — Cowork approval is the human gate.
• metrics() maps Dev.to fields → `PostMetrics` (impressions, replies, shares; clicks unavailable).
• Validation enforces Dev.to tag rules (`^[a-z0-9]+$`, ≤ 4 tags, ≤ 30 chars), 1-128 char title, https-only canonical URL.

Tests: 60/60 across 7 spec files (33 X + 27 Dev.to). All msw-mocked.

Build artifacts:

• `npx nx run marketing-channels:build` green
• `npx nx run marketing-channels:test` green (60 tests)
• `npx nx run website:build` green
• `DRY_RUN=1 pnpm marketing:channels:devto:smoke` green

Known follow-up (not blocking this PR):

• `DevToAdapter` constructor throws on missing `DEVTO_API_KEY` before the dry-run guard in `postDevTo`, so dry-run requires a placeholder value in `.env`. Same architectural pattern as `XAdapter`. Worth a tiny refactor to short-circuit env requirements when `DRY_RUN=1`. Filing as a follow-up rather than expanding this PR's scope.

Manual smoke required before merge:

• Get a Dev.to API key at https://dev.to/settings/extensions, paste `DEVTO_API_KEY=` into `.env`
• Run: `pnpm marketing:channels:devto:smoke`
• Confirm the post lands on Dev.to, then delete it

Spec: `docs/superpowers/specs/marketing/2026-05-17-channel-adapter-devto-design.md`
Plan: `docs/superpowers/plans/marketing/2026-05-17-channel-adapter-devto.md`

Test plan

• Build green
• Tests green (60/60)
• Website build green
• Dry-run smoke green
• Brian runs live Dev.to smoke; result pasted below

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
cacheplane	Ready	Preview, Comment	May 18, 2026 7:47pm

[blove]

Live smoke ✅

Ran pnpm marketing:channels:devto:smoke against Brian's Dev.to account.

{
  "channel": "devto",
  "postId": "3695562",
  "url": "https://dev.to/blove/marketing-pipeline-smoke-test-2026-05-18t195042132z-46gl",
  "postedAt": "2026-05-18T19:50:42Z"
}

Metrics: {
  "postId": "3695562",
  "impressions": 0,
  "replies": 0,
  "shares": 0,
  "fetchedAt": "2026-05-18T19:50:47.715Z"
}

Both post() and metrics() work end-to-end against the live API. Counts are 0 because the article is fresh; field mapping is correct. Test article will be deleted from Dev.to. Auto-merge enabled.