fix(updates): Keep bundle identity as PostHog Code

[charlesvien]

Problem

v0.58.0 shipped the #3557 rename with productName/executableName changed to "PostHog". Squirrel.Mac names the installed bundle after the update payload and relaunches the pre-update bundle path, so every install that auto-updates gets moved to /Applications/PostHog.app, fails to relaunch, and leaves the old Dock pin pointing at a dead path.

Changes

Minimal revert of the two identity fields to "PostHog Code", frozen with a comment the same way appId is, plus the handful of harness/docs paths that reference the built bundle. Display strings from #3557 are untouched. The next release's payload is named PostHog Code.app again, so v0.57.x installs update cleanly; the v0.58.0 cohort gets renamed back on their next update (one manual relaunch, same as they already hit).

Follow-ups deliberately NOT in this PR: v0.58.0 should be pulled from the update feeds so v0.57.x stragglers stop updating into the broken state, and a proper display-only rename (CFBundleDisplayName) plus Dock-pin repair can come separately.

How did you test this?

• tsc --noEmit and Biome clean on the touched files.
• Not yet exercised: a packaged build + the update e2e against this branch; update e2e baseline run against renamed main is in flight (run 29901251314) to confirm the failure mode this reverts.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 0e548a0.}