feat: console.log prints booleans/null correctly, fix JSON.stringify format

[cs01]

Summary

• console.log(true) now prints true instead of 1, console.log(false) prints false instead of 0
• console.log(null) prints null, console.log(undefined) prints undefined (node compiler)
• JSON.stringify(true) returns "true" instead of "1.000000", JSON.stringify(false) returns "false"
• JSON.stringify(42) returns "42" instead of "42.000000" (fixed format from %f to %.15g)
• JSON.stringify(null) returns "null" (node compiler)
• Boolean variables from function returns also print correctly

Test plan

• New test: console-log-types.ts — boolean literals and variables
• New test: json-stringify-bool-null.ts — boolean and number format verification
• All 465 existing tests pass
• Self-hosting verification passes (Stage 0 + Stage 1)

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