docs(steps-06-09): wrap manifest tags onto multiple lines

[Pierre Malarme (pmalarme)]

What

The metadata.tags flow sequence in the step 06–09 manifest snippets had grown long enough to force horizontal scrolling in the rendered README.md code blocks. This converts it to a YAML block list (one tag per line) and keeps the solutions in sync.

• .workshop/docs/steps/06-skills.md (both the Part A and Part B deltas), 07-multi-agent.md, 08-workflow.md, 09-memory.md
• Matching .workshop/solutions/{06-skills,07-multi-agent,08-workflow,09-memory}/travel_assistant/agent.manifest.yaml

Also fixes a small accuracy gap in the step 6 Part A delta: it jumped straight from tool_declarations: to resources: [], hiding the fact that a template: block sits between them. It now carries an elision comment. The comment is deliberately left at top level rather than written as template: + comment, because a key with only a comment under it parses as template: null — which would drop the block for anyone pasting the delta wholesale.

Not changed

• Tag values and order are untouched everywhere — the change is purely formatting.
• Step 7's doc snippet still omits Foundry Skills while the step 7 solution includes it. That is pre-existing and correct: Part B of step 6 is optional, and the solutions represent the completed-Part-B path.
• Steps 02–05 docs already use block lists; only their solution manifests still use the flow form. Harmless, and out of scope here.

Validation

• All four solution manifests parse with PyYAML and are semantically identical to main; cumulative tag growth verified (05→06 adds Skills/Foundry Skills, →07 Multi-Agent, →08 Workflows, →09 Memory).
• python .workshop/scripts/lint_steps.py → 0 failures (2 pre-existing warnings).
• python -m pytest .workshop/scripts/tests → 154 passed.
• python .workshop/scripts/render_readme.py --step N renders cleanly for steps 6–9.
• No tooling matches on the literal tags: [. Root README.md and .workshop_instance/ are untouched.