fix(iris): binary-safe base64 decoding for profile downloads

[rjpower]

Fix binary data corruption in memray .bin downloads. The download path used atob() → Blob([string]), which UTF-8 encodes the string and corrupts non-ASCII bytes. Now uses Uint8Array to preserve raw bytes.

Followup to #4415.

Generated with Claude Code

[claude]

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PR Review: Binary-safe base64 decoding for profile downloads

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Verdict: Looks good. The fix is correct — atob() returns a "binary string" where each char is 0–255, but passing that string directly to Blob re-encodes it as UTF-8, corrupting any byte ≥ 0x80. The Uint8Array + charCodeAt pattern is the standard workaround.

Two minor observations:

1. Duplicated decode logic in JobDetail.vue: The inline decode in JobDetail.vue:425-429 duplicates the new base64ToBytes() helper in useProfileAction.ts. Consider importing and reusing base64ToBytes to keep one implementation. Fix this →

2. Thread dump path still uses atob directly (useProfileAction.ts:31): This is fine since thread dumps are text (UTF-8 safe), but worth a brief inline comment noting why atob is safe there vs. the binary path, to prevent a future reader from "fixing" it to use base64ToBytes and then rendering it as bytes instead of a string.

Otherwise the change is clean and well-scoped. 👍