Raise JaCoCo coverage floor above 50% line / 30% branch

[devops-thiago]

Background

pom.xml enforces a whole-project JaCoCo floor of 50% line / 30% branch coverage, explicitly commented as "set just below current levels (line ~53%, branch ~34%); raising these as coverage improves is a follow-up."

Impact

• The quality gate passes with roughly half the code untested.
• Key RAG paths (retrieval filtering, token tracking, provider factories, error branches) may be under-tested without anyone noticing.
• Codecov/SonarCloud badges imply higher coverage than the gate actually enforces.

How to reproduce

1. Run mvn jacoco:check — passes at the 50%/30% floor.
2. Delete a test exercising a covered branch and re-run — still passes until coverage dips below the floor.

Where the fix should land

Raise the floor incrementally as coverage improves:

• Measure current coverage (mvn clean test jacoco:report).
• Raise the BUNDLE limits in pom.xml in steps (e.g. 0.55/0.35, then 0.60/0.40) rather than one big jump.
• Add focused unit tests for under-covered classes (TokenUsageTracker, MetricsService, VectorRepositoryFactory, provider error paths) to keep pace with each raised floor.

Files touched

• pom.xml (JaCoCo configuration/rules)
• New/updated tests under src/test/java/...

Acceptance criteria

• JaCoCo floor raised by at least one step and the CI code-coverage job stays green.
• Coverage improvement visible in the Codecov report.
• No tests skipped or disabled to game the threshold.