fix(agent): exclude vendored files from tech detection

[JohnsonGNEP]

Summary

Fixes tech stack detection so vendored, dependency, build-output, cache, virtualenv, and git metadata paths do not affect detected languages or the primary language. This prevents generated JavaScript files under paths like node_modules/ and build/ from making a mostly Python repo look like JavaScript.

Issue

Closes #150

Changes

• Normalize repository file paths before filtering.
• Skip files when any path part matches ignored directories such as node_modules, vendor, dist, or build.
• Count detected languages from filtered real source/config files.
• Add regression coverage for root-relative vendored and build-output paths.

Testing

• Unit tests pass (make test-unit)
• Integration tests pass (make test-integration)
• Linter passes (make lint)
• Type checker passes (make typecheck)
• New/updated tests cover the changes

Direct validation:

• ruff check agent/tools/tech_detector.py tests/unit/test_tech_detector.py
• python -m pytest tests/unit/test_tech_detector.py -v -m unit — 28 passed

Note: make is not installed in my local PowerShell environment. Running the equivalent repo-wide checks directly showed pre-existing unrelated failures outside this issue's files:

• ruff check . reports 173 unrelated lint issues.
• python -m pytest tests/unit -v -m unit reports 50 failed, 348 passed, and 31 errors in unrelated modules.

Screenshots / Demo

N/A

Notes for Reviewers

Please focus on agent/tools/tech_detector.py and tests/unit/test_tech_detector.py. The issue-specific lint and unit tests pass locally.

[JohnsonGNEP]

Hi! This PR is ready for review. The issue-specific lint and tests pass locally:

• ruff check agent/tools/tech_detector.py tests/unit/test_tech_detector.py
• python -m pytest tests/unit/test_tech_detector.py -v -m unit

I also documented the repo-wide pre-existing failures in the PR description.