fix(budgetManager): prevent cost accumulation past limit in warn mode

[Srejoye]

Problem

In warn mode, track() issued a console.warn() when the projected total exceeded the limit, but then fell through to this.totalSpent += cost. The cost was committed on every over-limit call, causing totalSpent and percentageUsed to grow without bound — making budget status meaningless.

Root Cause

src/core/budgetManager.ts → track(), lines 66–68. After console.warn(), there was no early exit. The this.totalSpent += cost on line 72 runs unconditionally for both modes after the if-block.

Fix

Add return after console.warn(message). The finally block still runs, so the async lock is correctly released. One line changed.

Behaviour

Scenario	Before	After
warn mode, over-limit call	cost committed, totalSpent grows	cost rejected, totalSpent frozen at limit
warn mode, percentageUsed after overrun	can exceed 100%	stays at limit value
block mode	throws, no change	throws, no change ✓
warn mode, under-limit calls	committed normally	committed normally ✓

Testing

• warn mode: totalSpent does not increase after limit is exceeded
• warn mode: percentageUsed stays at the limit percentage, not beyond
• warn mode: under-limit calls still accumulate normally
• block mode: still throws, completely unaffected
• async lock (releaseLock) still fires in all cases via finally

Closes #4