feat(subagents): add Reasonix native subagents adapter

[dyoshikawa]

Background

Reasonix supports native subagents, exposed as Skill profiles: directory-layout .reasonix/skills/<name>/SKILL.md files whose YAML frontmatter declares invocation: manual and runAs: subagent. rulesync already had Reasonix adapters for rules, commands, MCP, permissions, hooks, and skills, but reasonix was absent from the subagents feature, so rulesync generate --features subagents skipped it.

Primary source: SUBAGENT_PROFILES.md. The documented frontmatter is name, description, color, invocation: manual, runAs: subagent, model, effort, allowed-tools.

Change

• New ReasonixSubagent adapter (src/features/subagents/reasonix-subagent.ts), modeled on the directory-per-agent Devin adapter since the <name>/SKILL.md layout matches Devin's <name>/AGENT.md.
  • Always injects the invocation: manual / runAs: subagent markers on generate.
  • Maps model/effort/allowed-tools/color through the reasonix: tool-specific block; z.looseObject preserves unknown upstream keys on round-trip.
  • Same .reasonix/skills/ directory for project and global scope (supportsGlobal: true).
• Registered in the subagents tuple + toolSubagentFactories map, e2e project + global matrices, processor test target lists, tables (README / supported-tools), and file-formats.md (synced to skills/rulesync/).

Verification

• pnpm cicheck (code + content) green.
• e2e src/e2e/e2e-subagents.spec.ts green (project + global generate paths produce .reasonix/skills/planner/SKILL.md).

Closes #2235

[dyoshikawa]

⚠️ Do not merge as-is — this ships confirmed data loss.

Reasonix stores skills and subagents in the same directory/filename (.reasonix/skills/<name>/SKILL.md), split only by the runAs: subagent marker. Because rulesync treats skills and subagents as separate features with independent orphan-deletion, --delete on either feature removes the other's files (reproduced in both directions).

The adapter itself is complete and CI-green, but it needs marker-aware discovery + orphan-deletion on both this adapter and reasonix-skill.ts before it can safely land. See #2235 for the design decision. Holding this PR open pending that call.