Feat/issue 12 closure

[rosspeili]

Summary

Completes the reference ToolHost epic: AURA as a universal governance coat over any skill/tool host — with Skillware as one live reference adapter, not the product focus.

• Break observer preset — observer.alert on repeated tool intents; session preset: break ([Integration]: Break observer preset — runaway tool circuit breaker alerts #34)
• Ingress bind enrichment — host.bind, bound_skill_ids, session_snapshot_hash on skill.registered ([Integration]: Ingress context enrichment at session and skill bind #33)
• OTel promoted attributes — aura.agent_ref, aura.policy_version, aura.principal, aura.skill_id on spans ([Bug]: OTel export missing first-class principal and policy_version attributes #35)
• Sequencer when — conditional step skip with sequencer.step.skipped on the spine
• Capstone guide — reference-tool-host-capstone.md: 360° checklist for any ToolHost adapter (`[Integration]: Example 06 — reference tool-host pipeline with optional live Skillware #40)
• Examples 07–08 — observer presets tour, emit-only loose coat ([Enhancement]: Expand examples library after reference-host and flat layout #41 partial — flat restructure remains [Enhancement]: Restructure examples — flat named scripts and single README index #21)

Closes the reference-host acceptance path started in #42 (ToolHost protocol, manifest merge, monitor preset, registry loader, examples 05–06).

Fixes #12
Fixes #33
Fixes #34
Fixes #35
Fixes #40
Fixes #41
Fixes #16

Test plan

• pytest --ignore=tests/integration — 78 passed
• pytest tests/integration/ — 4 passed
• black / flake8 clean
• Example smoke auto-discovers 07–08 via tests/test_examples_smoke.py