feat(skills): remove interaction-skills; ship only BROWSER.md + cloud-browser.md

[Alezander9]

Summary

Evals show the agent rarely reads the 16 interaction-skills/*.md files
inherited from the Python harness era, and is performing well without them.
Pulling them out of the embedded skills tree so we can be data-driven about
what ships: reintroduce only the recipes evals show are needed, one at a
time, with before/after evidence.

What's left in skills/

• BROWSER.md — the agent's prompt for browser_execute (snippet model,
  three connection methods, workspace pattern, session API surface,
  guardrails, troubleshooting).
• cloud-browser.md — Way 3 cloud-browser provisioning recipe.

What moved out

packages/bcode-browser/skills/interaction-skills/ (16 files) is moved to
<workspace>/reference/interaction-skills/ on the maintainer's machine,
with a PROVENANCE.md noting origin and reason. Not committed anywhere —
kept as a private reference for picking what to restore.

In-repo edits

• skills/BROWSER.md — trimmed three references:
  • "Locations" bullet now lists the two remaining skills explicitly.
  • "The model in one paragraph" drops the trailing skills-as-docs sentence.
  • The standalone "For the full menu of UI mechanics …" paragraph is gone.
  • The iframe/shadow-dom troubleshooting bullet now inlines the CDP
    one-liner (Page.getFrameTree/element.shadowRoot.querySelector)
    instead of pointing at deleted skill files.
• packages/opencode/src/tool/browser-execute.txt — drops the trailing
  "For UI-mechanic recipes …" paragraph.
• packages/opencode/src/tool/browser-execute.ts — comment updated to say
  BROWSER.md / cloud-browser.md instead of the old interaction-skills
  reference.
• packages/bcode-browser/src/index.ts — comment for skills/ updated.
• packages/bcode-browser/README.md — skills/ row updated; one-sentence
  note about the archival decision.
• packages/bcode-browser/test/skills.test.ts:
  • Removed the interaction-skills substring assertion.
  • Normalized the cloud-browser.md assertion to be cross-platform
    (the original used path.join which doesn't match the forward slash
    baked into {{SKILLS_DIR}}/cloud-browser.md after substitution on
    Windows). Drive-by fix; same intent.

Out of scope

UPSTREAM.md §3 and AGENTS.md "Vendored harness" still reference an
interaction-skills/ path under the (already-retired) Python harness.
That whole section is stale post Phase H and unrelated to this change —
will be cleaned up separately.

Verification

• bun test test/skills.test.ts test/browser-execute.test.ts — 4 pass /
  6 skip (chrome smoke gated on BCODE_SMOKE_CHROME=1) / 0 fail.
• bun typecheck clean in packages/bcode-browser and packages/opencode.

22 files changed, 11 insertions(+), 5 deletions(-) for code; 16 deletions
under skills/interaction-skills/ for the archived files.

[cubic-dev-ai]

No issues found across 22 files