feat: add Maven command filter

[rmarioo]

Summary

• Add rtk mvn command filter for Maven build and test output
• Achieves 60-90% token savings by extracting only errors, failures, and summaries
• Supports mvn compile, mvn test, mvn package, mvn install, mvn clean, and other Maven goals
• Adds Maven to discover rules for automatic detection

Changes

• src/mvn_cmd.rs (new): Maven command filter with build error extraction, test failure parsing, and summary condensing
• src/main.rs: Register Mvn command variant and routing
• src/discover/rules.rs: Add Maven discovery rule
• README.md: Document Maven support and token savings
• tests/fixtures/: Real Maven build and test output fixtures

Test plan

• 14 unit tests covering build success/failure, test success/failure, edge cases
• Token savings verified ≥60% on real Maven output
• cargo fmt --check passes
• cargo clippy — 0 errors (warnings are pre-existing)
• All 777 existing tests still pass (1 pre-existing failure unrelated to this PR)

🤖 Generated with Claude Code

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[pszymkowiak]

Hi! Two things needed before we can review:

1. Retarget to develop — this PR targets master, but all PRs should target develop. You can change the base branch in the PR settings (right sidebar).
2. Sign the CLA — if not already done, please sign at https://cla-assistant.io/rtk-ai/rtk

Thanks!

[aeppling]

Hey

We are cleaning up the codebase and improving the project structure for better onboarding. As part of this effort, PR #826 reorganizes src/ from a flat layout into subfolders.

No logic changes — only file moves and import path updates.

What you need to do

Rebase your branch on develop when receiving this comment:

git fetch origin && git rebase origin/develop

Git detects renames automatically. If you get import conflicts, update the paths:

use crate::git;        // now: use crate::cmds::git::git;
use crate::tracking;   // now: use crate::core::tracking;
use crate::config;     // now: use crate::core::config;
use crate::init;       // now: use crate::hooks::init;
use crate::gain;       // now: use crate::analytics::gain;

Need help rebasing? Tag @aeppling