feat(skills): populate every detected runtime's skills dir

[chubes4]

Summary

Closes #63.

Runtime auto-detection in setup.sh (and upgrade.sh) was single-pick, first-match-wins:

if   command -v studio &>/dev/null && [ "${IS_STUDIO:-false}" = true ]; then RUNTIME=studio-code
elif command -v claude &>/dev/null;                                          then RUNTIME=claude-code
elif command -v opencode &>/dev/null;                                        then RUNTIME=opencode
fi

On a machine with both claude and opencode installed, cascade picked claude-code silently. SKILLS_DIR="$(runtime_skills_dir)" resolved to a single runtime's dir (.claude/skills/ vs .opencode/skills/), so ./setup.sh --skills-only only ever populated one runtime. To get skills into the other runtime users had to re-run with explicit --runtime opencode.

Fix

Track all detected runtimes in a new DETECTED_RUNTIMES[] array alongside the existing primary RUNTIME. In install_skills and print_skills_summary, iterate every detected runtime, resolve its skills dir, and install into each unique dir.

setup.sh / upgrade.sh

• New DETECTED_RUNTIMES=() array populated during auto-detect (studio-code → claude-code → opencode, keeps existing cascade order).
• RUNTIME="\${DETECTED_RUNTIMES[0]}" — primary stays first-match.
• Explicit --runtime <name> narrows both lists to the single runtime (preserves single-runtime-mode for users who want it).

lib/skills.sh

• New _resolve_skills_dir_for_runtime() helper sources a runtime file in a subshell and echoes its runtime_skills_dir. Avoids polluting the primary runtime's functions.
• install_skills builds a unique list of skills dirs across DETECTED_RUNTIMES (de-duped — claude-code and studio-code both resolve to \$SITE_PATH/.claude/skills) and installs into each.
• Primary SKILLS_DIR is restored at the end so the kimaki mirror source, persistent-source mirror, and summary output keep working against the primary runtime's dir.
• print_skills_summary now lists every populated dir.

The primary RUNTIME still drives runtime_install, runtime_generate_config, runtime_install_hooks, and the chat-bridge default — nothing else changes in the single-runtime path.

Testing

• bash -n setup.sh upgrade.sh lib/skills.sh — passes.
• tests/bridge-render.sh — all 8 snapshots byte-identical.
• Dry run with both claude and opencode on PATH:

  Phase 8.5: Installing agent skills...
    Detected 2 runtime(s): claude-code opencode
    Populating 2 unique skills dir(s)
  → Installing skills into /Users/chubes/Studio/intelligence-chubes4/.claude/skills
  → Installing skills into /Users/chubes/Studio/intelligence-chubes4/.opencode/skills
  

• Real run on `intelligence-chubes4`: both .claude/skills/ and .opencode/skills/ populated with all 5 skills. Kimaki mirror (\$(npm root -g)/kimaki/skills/) and persistent source (~/.kimaki/kimaki-config/skills/) still single-sourced from the primary runtime's dir as before.
• Single-runtime override: --runtime claude-code reduces back to just .claude/skills/ with no multi-runtime banner.

AI assistance

• AI assistance: Yes
• Tool(s): Claude Code (Opus 4.7)
• Used for: drafted the DETECTED_RUNTIMES model, subshell-based skills-dir resolver, and the de-dup logic. Chris reviewed and validated multi-runtime population end-to-end on his Studio install (both .claude/skills/ and .opencode/skills/ populated in a single run).