fix(gui): repair log tooltip encoding

[olddonkey]

Summary

• Replace malformed UTF-8 byte escapes in Logs model and token tooltips with a single Unicode middle dot, eliminating visible · mojibake.
• Extract tooltip formatters for direct regression coverage.
• Add a GUI source encoding hygiene test that rejects invalid UTF-8, common mojibake, and adjacent multibyte \xNN escape sequences.

Screenshots

Model tooltip (before)

Token tooltip (before)

Verification

• bun run typecheck
• bun run test — 12,753 pass / 10 skip / 0 fail
• cd gui && bun test tests — 939 pass / 0 fail
• cd gui && bun run lint
• cd gui && bun run build
• bun run privacy:scan
• git diff --check

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed. (Not needed: no configuration or workflow change.)
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults. (No security-sensitive surface changed.)

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• I resolved all correct Codex and CodeRabbit findings.

• My PR is ready for review.

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[github-actions]

⏳ DRAFT

• review readiness checklist open (0/4 boxes ticked).

What to do

• Tick all four boxes in the PR description once you're done (currently 0/4).

Review readiness checklist

• ⬜ All CI tests are green on my local testing.
• ⬜ I pushed my PR to the latest dev commit.
• ⬜ I resolved all correct Codex and CodeRabbit findings.
• ⬜ My PR is ready for review.

0/4 boxes ticked.

This PR stays in draft until every box above is ticked.