ui: Icicle chart minor UX tweaks

[manojVivek]

Contains:

• Hide the "root" node in Flamecharts
• Disable click interactions in Flamecharts

[alwaysmeticulous]

✅ Meticulous spotted zero visual differences across 224 screens tested: view results.

Meticulous simulated ~4 hours of user flows against your PR.

_{Expected differences? Click here. Last updated for commit 0de5293. This comment will update as new commits are pushed.}