fix(mcp): keep tag values verbatim in nostr_publish_event

[tcheeric]

Summary

nostr_publish_event dropped empty tag values and trimmed the others. NIP-01 tags are positional, so ["p", pk, "", "mention"] was signed and published as ["p", pk, "mention"]: the marker landed in the relay-hint slot, and the event that went out was not the one previewed for approval.

Found in production: a NIP-84 highlight's recomputed id didn't match the approved event file, and diffing the live event against it showed the shifted p tag.

Type of change

• fix - Bug fix (non-breaking)
• test - Adding or updating tests
• chore - Build, CI, or tooling changes (version bump to 2.4.1)

What changed?

• ToolArguments.nestedTexts() reused texts(), which trims values and filters out empty strings. That is right for flat lists (ids, relays), wrong for tags. It now maps inner values with String::valueOf and nothing else. texts() is unchanged for its other callers.
• nestedTexts() has one caller, PublishEventTool, so nothing else is affected.
• New ToolArgumentsTest: empty values keep their position, values aren't trimmed, and the flat-tag path behaves the same.
• Release: all modules 2.4.0 → 2.4.1, CHANGELOG [2.4.1] section, docs version reference.

Testing

• Unit tests pass: mvn clean test (the three new tests failed before the fix)
• Integration tests pass: mvn verify (requires Docker), not run locally
• Installed the rebuilt jar as the local MCP server.

Review focus

Targets main rather than develop, matching #557: develop is still at 2.3.1 and doesn't contain 2.4.0.

Checklist

• PR title follows conventional commits: type(scope): description
• Changes are focused and under 300 lines
• Tests added/updated
• No new compiler warnings introduced
• CHANGELOG.md updated

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