Optimize add-provider dialog state derivation

[cursor]

What Changed

• Removed the add-provider dialog's reset and auto-derived instance-id useEffect chain.
• Render the dialog's stateful content only while open so each open starts from fresh state without a cascading reset effect.
• Derive the instance id during render until the user manually edits it, avoiding an extra render after every label/driver change.
• Added react-scan before/after recordings:
  • docs/perf-recordings/add-provider-dialog-before-react-scan.webm
  • docs/perf-recordings/add-provider-dialog-after-react-scan.webm

Why

React Doctor flagged AddProviderInstanceDialog for both cascading state updates in an effect and an effect chain derived from driver/label. This change follows React's "You Might Not Need an Effect" guidance by replacing derived state synchronization with render-time derivation and state ownership scoped to the open dialog content.

React Doctor result improved from 68/100 to 69/100, reducing total findings from 763 to 760 and state/effects findings from 28 to 26. The add-provider dialog no longer appears in react-doctor/no-effect-chain or react-doctor/no-cascading-set-state.

UI Changes

No intended visual UI changes. Interaction recordings with react-scan enabled are included in this PR:

• Before: docs/perf-recordings/add-provider-dialog-before-react-scan.webm
• After: docs/perf-recordings/add-provider-dialog-after-react-scan.webm

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Verification:

• bun fmt
• bun lint (passes with existing warnings)
• bun typecheck
• bunx react-doctor@latest apps/web --verbose --offline --fail-on none

  

Note

Optimize state derivation in AddProviderInstanceDialog by removing useEffect resets

• Extracts dialog logic into a new AddProviderInstanceDialogContent child component that only mounts when the dialog is open, replacing useEffect-driven form resets with natural unmount/remount behavior.
• Replaces the instanceId/instanceIdDirty state pair and its two useEffect hooks with a single manualInstanceId state and a derived instanceId computed as manualInstanceId ?? deriveInstanceId(driver, label).
• Adds before/after React Scan performance recordings under docs/perf-recordings/.

^{Macroscope summarized f991605.}