docs: add concurrent data migration procedure guide

[ctron]

Summary

• Add a step-by-step procedure for running data migrations with concurrency on a pre-existing database copy
• Cover environment variables, single-runner and multi-runner examples, and the full skip-then-migrate workflow
• Include a complete Kubernetes Job manifest (secrets, indexed parallel data migration jobs, schema migration job with MIGRATION_DATA_SKIP)
• Add navigation entries for data.adoc and the new guide in nav.adoc

Test plan

• Review rendered AsciiDoc for correctness
• Verify env var names match migration/src/data/mod.rs (Options struct)
• Verify CLI invocations match trustd/src/db.rs
• Verify migration names match migration/src/lib.rs

🤖 Generated with Claude Code

Summary by Sourcery

Add documentation for running concurrent data migrations and link it into the migration docs navigation.

Documentation:

• Introduce a detailed guide for concurrent data migrations, including environment configuration, workflows, and Kubernetes examples.
• Add navigation entries to expose the concurrent data migration guide and related data migration docs in the migration book.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds a new AsciiDoc guide describing how to run concurrent data migrations against a copied production database, and wires it into the existing migration docs navigation.

File-Level Changes

Change	Details	Files
Introduce a detailed concurrent data migration procedure guide in the migration docs.	Create a new AsciiDoc page explaining concurrent data migration on a pre-existing database copy Document required environment variables, mapping them to existing migration options Provide single-runner and multi-runner CLI invocation examples aligned with current binaries Describe the skip-then-migrate workflow using MIGRATION_DATA_SKIP and related flags Include full Kubernetes Job manifest examples for parallel data migrations and schema migrations	docs/book/modules/migration/pages/concurrent-data-migration.adoc
Update migration documentation navigation to expose the data migration docs and the new concurrent migration guide.	Ensure data.adoc is linked from the migration navigation structure Add an entry for the new concurrent-data-migration guide to nav.adoc Position the new guide logically among existing migration docs for discoverability	docs/book/modules/migration/nav.adoc

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[sourcery-ai]

Hey - I've left some high level feedback:

• In the new concurrent data migration guide, consider cross-linking more explicitly to the existing data.adoc page so readers can easily understand how the concurrent workflow builds on the baseline data migration concepts.
• For the Kubernetes Job manifest example, it may help to clearly mark customizable fields (e.g., image name, namespace, resource requests/limits, secret names) so operators can better distinguish between required values and example placeholders.
• Where you describe single-runner vs multi-runner concurrency, consider calling out any ordering or idempotency assumptions of individual migrations so users understand when parallel execution is safe and when it is not.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In the new concurrent data migration guide, consider cross-linking more explicitly to the existing `data.adoc` page so readers can easily understand how the concurrent workflow builds on the baseline data migration concepts.
- For the Kubernetes Job manifest example, it may help to clearly mark customizable fields (e.g., image name, namespace, resource requests/limits, secret names) so operators can better distinguish between required values and example placeholders.
- Where you describe single-runner vs multi-runner concurrency, consider calling out any ordering or idempotency assumptions of individual migrations so users understand when parallel execution is safe and when it is not.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.33%. Comparing base (0bb3674) to head (9fbd3c1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2421      +/-   ##
==========================================
+ Coverage   71.30%   71.33%   +0.02%     
==========================================
  Files         450      450              
  Lines       27164    27191      +27     
  Branches    27164    27191      +27     
==========================================
+ Hits        19370    19397      +27     
+ Misses       6663     6656       -7     
- Partials     1131     1138       +7     

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