feat: add no-unrestricted-loop-in-serverless lint rule

[danielchen0]

Summary

• Adds no-unrestricted-loop-in-serverless rule that detects unbounded loops (while(true), for(;;), while(1)) without a break or return in the loop body
• These loops cause Vercel 300s timeouts in serverless functions — 21K+ timeouts/week in production
• Smart about scope: doesn't count break inside nested loops/switches, or return inside nested arrow functions (e.g. .map() callbacks)
• Allows loops that have proper exit conditions (break, return, bounded test)
• Platform: backend only

Test plan

Scenario	Expected
while (true) { await fetchData(); } (no break)	Error flagged
for (;;) { await poll(); } (no break)	Error flagged
while (1) { doWork(); } (no break)	Error flagged
while (true) { if (done) break; }	No error
while (true) { if (done) return data; }	No error
for (let i = 0; i < 100; i++) { ... }	No error
while (count < 10) { ... }	No error
while (true) { for (...) { break; } } (break in nested loop)	Error flagged (break doesn't exit outer)
while (true) { data.map(x => { return x; }) } (return in nested fn)	Error flagged (return doesn't exit loop)