feat(workshops/legacy-modernization): add platform story coverage + delivery variants

[devin-ai-integration]

Summary

Adds platform story coverage to the legacy modernization workshop — a ## Platform Context section, cross-surface callout blocks in README.md, and a new README.platform.md Desktop + Cloud delivery variant.

README.md (cloud-agent baseline) changes:

• Variant header note linking to README.platform.md
• ## Platform Context section after Overview explaining this is a Devin Cloud / web-app workshop, with a > **Tip:** callout pointing to the Desktop variant
• Agent Command Center bullet in the "Getting the Most" tips section
• > **Desktop tip:** callouts after Labs A1, A4, B1, B4 (PR review via one-click checkout, ACC monitoring)
• > **CLI alternative:** callouts after Labs A3, B3 (local iteration for test harness exploration)
• No changes to existing lab structure, prompts, track numbering, timing, or content

README.platform.md (new — Desktop + Cloud variant):

• Reframes the entire workshop for participants using Devin Desktop as their primary interface
• Replaces the 4-step web-app workflow (paste prompt → Ask Devin → DeepWiki → review PR) with a 5-step Desktop workflow:
  1. Create a Space for the workshop
  2. Explore locally with Cascade / Devin Local
  3. Delegate to Devin Cloud from Desktop
  4. Monitor in the Agent Command Center (Kanban board)
  5. Review with one-click checkout in the editor
• Same lab structure: Track A (A1-A4), Track B (B1-B4), identical prompts and target outcomes
• References ACP and multi-agent usage where relevant (parallel cloud sessions, child agents for migration campaigns)
• Added a sixth Key Takeaway: "Local exploration, cloud execution"

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/1a57f1babf724765a178eddf89921121
Requested by: @bsmitches

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[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 1 potential issue.

View 2 additional findings in Devin Review.

[devin-ai-integration]

🚩 Broken internal link to non-existent cobol-modernization-workshop event directory

Both workshops/legacy-modernization/README.md:68 and the new workshops/legacy-modernization/README.platform.md:82 link to ../../events/cobol-modernization-workshop/README.md, but the directory events/cobol-modernization-workshop/ does not exist in the repo. Only events/oracle-forms-modernization-workshop/ exists. This is a pre-existing issue (present in the base branch README.md at lines 59 and 308) that is carried forward into the new platform variant file. It's likely a placeholder for a planned-but-not-yet-created event directory, so it may be intentional — but readers clicking the link will get a 404.

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[devin-ai-integration]

Confirmed — this link is pre-existing in the base branch README.md (lines 59 and 308). The events/cobol-modernization-workshop/ directory doesn't exist yet; it's likely a planned placeholder. The new README.platform.md carries the same link forward for consistency. Fixing or removing it is out of scope for this PR.