[AAASM-2290] 📝 (README): Highlight audit-trace, budget-limits, sidecar-runtime as advanced scenarios

[Chisanan232]

What changed

Updated the root README.md in three commits:

1. Quick navigation table — replaced the generic "See audit trace and budget controls" row with three specific direct links to scenarios/audit-trace/, scenarios/budget-limits/, and scenarios/sidecar-runtime/.

2. Advanced scenarios section — added a new ## Advanced scenarios: observability and runtime controls section (with a table showing each scenario, what it demonstrates, and a quick-start command) positioned before ## Prerequisites so it's visible near the top of the page.

3. Repository layout — expanded the scenarios/ block in the layout tree to list the three new subdirectories with brief annotations.

Related ticket

Closes #AAASM-2290

How to verify

Read the updated README.md and confirm:

• Quick navigation table has three scenario-specific rows
• ## Advanced scenarios section is present with the three-row table
• Repository layout shows audit-trace/, budget-limits/, sidecar-runtime/

Checklist

• PR title follows [AAASM-XXXX] <GitEmoji> (<scope>): <summary>
• No secrets, API keys, or .env files committed
• Example sub-projects include their own README.md with prerequisites and run instructions
• SDK/runtime version dependencies are documented or pinned

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Chisanan232]

Code Review — Claude Code

Scope review result: ✅ Ready to merge

CI status

Check	Result
build	✅ pass
run	✅ pass
SonarCloud	✅ pass

Coverage against AAASM-2290 / AAASM-2197 AC-6

Requirement	Status
Quick navigation table — specific links to audit-trace/, budget-limits/, sidecar-runtime/	✅ 3 new rows added
## Advanced scenarios section with table (scenario, what it demonstrates, quick-start command)	✅ section present before ## Prerequisites
Each scenario's quick-start command is correct	✅ python scenarios/audit-trace/python/agent.py etc.
Repository layout updated to list new subdirectories	✅ 3 lines added under scenarios/
No existing content broken	✅ diff is purely additive

Observations

• Positioning the "Advanced scenarios" section before ## Prerequisites means it's visible immediately after the quick-nav table — correct placement for discoverability.
• The table uses relative links (./scenarios/audit-trace/) which will render correctly on GitHub even after the repo is cloned or forked.
• The repository layout additions are concise annotations, consistent with the existing layout style.

No issues found. Approved from scope and correctness standpoint.