Issue 11: Separate transient task instructions from keepable skills

[gewenyu99]

Issue 11: Separate transient task instructions from keepable skills

Epic: Task-queue orchestrator runner · Depends on: #624, #627

Why

The orchestrator installs a mini-skill per task — install, init, identify,
capture, error-tracking-step, build, dashboard, report — into
.claude/skills/ (via installSkillById in the executor's runTask). These are
the procedural HOW each task agent follows: transient wizard instructions, not
durable skills a user would keep for ongoing agent work.

But they land in the same .claude/skills/ directory as the linear flow's
keepable integration skill, so the keep-skills outro screen lists all eight
and offers to keep them. That is wrong twice over: it clutters the user's project
with eight one-shot instruction folders, and it frames throwaway scaffolding as
something worth keeping.

The linear flow has one durable skill (e.g. integration-nextjs-app-router) that
is genuinely worth keeping. The orchestrator has none — every skill it pulls is
scaffolding for a single run.

Scope / deliverable

1. Install task instructions to an ephemeral location, not .claude/skills/.
   installSkillById already takes a skillsRoot override (the reference-example
   install uses .posthog-wizard/reference/). Install the per-task mini-skills
   under the run dir, e.g. .posthog-wizard/skills/<type>/, so they never touch
   .claude/skills/.
2. Auto-delete them at run end. The whole .posthog-wizard/ working area is
   already the orchestrator's scratch space; clean up the installed task skills
   when the run finishes (success or failure), the same way the reference example
   is throwaway.
3. Keep them out of the keep-skills screen. With the instructions no longer in
   .claude/skills/, the keep-skills step naturally has nothing orchestrator-owned
   to offer. Confirm the orchestrator arm either skips the keep-skills screen
   entirely (it installs no durable skill) or only ever surfaces a genuinely
   keepable skill, never the task instructions.

Key files

• src/lib/programs/orchestrator/orchestrator-runner.ts — runTask installs each
  task's skills; point them at an ephemeral skillsRoot and clean up on run end.
• src/lib/wizard-tools.ts — installSkillById(..., skillsRoot?) already supports
  the override.
• the keep-skills TUI step / screen — confirm it reads .claude/skills/ and so
  shows nothing once the instructions install elsewhere.

Acceptance criteria

• An orchestrator run installs no mini-skills into .claude/skills/; the task
  instructions live under .posthog-wizard/ and are gone after the run.
• The keep-skills outro screen does not list install, capture, build,
  etc. — it offers nothing for the orchestrator arm (or only a real keepable
  skill, if one is ever introduced).
• With the flag off, the linear keep-skills behaviour is unchanged.
• No leftover .posthog-wizard/skills/ after a clean run.

[gewenyu99]

Shipped via #637 (Closes #632) — task mini-skills install under .posthog-wizard/skills (never .claude/skills) and the whole scratch dir is rm'd at run end; GitHub state was stale.