Add SQLite FTS5-backed ToolStore for optimizer search

[aponcedeleonch]

Closes: #3731

Add an SQLite FTS5 ToolStore implementation as an alternative to the existing InMemoryToolStore, and wire it into the vMCP server when optimizer config is present.

This adds:

• pkg/vmcp/optimizer/fts5store: SQLiteToolStore implementation using modernc.org/sqlite (pure Go, no CGO) with FTS5 virtual tables
• BM25 ranking for search results with LIKE-based fallback
• FTS5 query sanitization for safe handling of special characters
• Thread-safe concurrent access with sync.RWMutex
• Close() method on the ToolStore interface for resource cleanup
• OptimizerStoreCloser on server.Config for store lifecycle management
• OptimizerConfig.FTSDBPath for configurable database location (defaults to in-memory, use emptyDir in Kubernetes)
• Wire FTS5 store into vMCP serve command when optimizer is configured
• Comprehensive tests for search, upsert, and concurrency scenarios

Part 2 of the optimizer FTS5 migration (issue #3731).

Large PR Justification

• Multiple related changes that would break if separated. It just introduces 1 new concept

[github-actions]

Large PR Detected

This PR exceeds 1000 lines of changes and requires justification before it can be reviewed.

How to unblock this PR:

Add a section to your PR description with the following format:

## Large PR Justification

[Explain why this PR must be large, such as:]
- Generated code that cannot be split
- Large refactoring that must be atomic
- Multiple related changes that would break if separated
- Migration or data transformation

Alternative:

Consider splitting this PR into smaller, focused changes (< 1000 lines each) for easier review and reduced risk.

See our Contributing Guidelines for more details.

---

This review will be automatically dismissed once you add the justification section.

[codecov]

Codecov Report

❌ Patch coverage is 78.43137% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.86%. Comparing base (471f878) to head (85a4c84).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
...cp/optimizer/internal/sqlite_store/sqlite_store.go	75.94%	10 Missing and 9 partials ⚠️
pkg/vmcp/server/server.go	75.00%	1 Missing and 1 partial ⚠️
cmd/vmcp/app/commands.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3786      +/-   ##
==========================================
+ Coverage   66.81%   66.86%   +0.04%     
==========================================
  Files         438      439       +1     
  Lines       43321    43404      +83     
==========================================
+ Hits        28946    29020      +74     
- Misses      12128    12132       +4     
- Partials     2247     2252       +5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jerm-dro]

I'll take a closer look at the sqlite_store_test when they're in a more condensed form. Everything else looks mostly good aside for some blocking comments which should be easy to address.

Large PR justification has been provided. Thank you!

[github-actions]

✅ Large PR justification has been provided. The size review has been dismissed and this PR can now proceed with normal review.

[jerm-dro]

One minor blocker, but otherwise LGTM

[jerm-dro]

feel free to address the nit in a later PR