Add memo support to Start Workflow

[dieend]

Description & motivation 💭

Adds a JSON Memo field to the Start Workflow page so workflows that require memo metadata can be started from the UI. “Start Workflow Like This One” now decodes and prefills memo fields from the source execution.

Screenshots (if applicable) 📸

N/A

Design Considerations 🎨

Memo input is represented as a JSON object. Each top-level value is encoded as a Temporal payload before the start request is sent.

Testing 🧪

How was this tested 👻

• Manual testing
• E2E tests added
• Unit tests added

Validated with the focused workflow-service unit tests, ESLint, Prettier, and Svelte check (0 errors). Integration coverage was added for the memo field and validation; local Playwright execution was blocked in global setup by an unrelated @temporalio/common encode is not a function error before tests ran.

Steps for others to test: 🚶🏽‍♂️🚶🏽‍♀️

1. Open Start Workflow and expand More options.
2. Enter a JSON object in Memo and start the workflow.
3. Verify the new execution contains those memo fields.
4. From an execution with memo fields, choose Start Workflow Like This One and verify Memo is prefilled.

Checklists

Draft Checklist

• Implementation and automated coverage included

Merge Checklist

• CI passes
• Review complete

Issue(s) closed

Closes #2512

Docs

Any docs updates needed?

No documentation updates are required.

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