fix(tui): replace @solid-primitives/scheduled with manual debounce for Node.js compatibility

[malventano]

@solid-primitives/scheduled returns a no-op when isServer=true. The conditions: ["node"] build change (commit 1e216e1, #30873) resolves solid-js/web to server.js, setting isServer=true. This breaks:

• Session search in /sessions dialog (both basic list and experimental switcher) — search input does not filter results
• Session switcher preview pane — preview freezes after first hover

Solution

Replace @solid-primitives/scheduled with manual setTimeout:

• signal.ts — createDebouncedSignal → manual trailing-edge debounce
• preview-pane.tsx — createLeadingTrailingSignal → manual leading + trailing edge

No build condition changes. No skipFilter changes. Fix isolated to two utility files.

Tradeoffs

• Loses clear() method and automatic onCleanup (neither currently used)
• Does not fix upstream — this is a local workaround for TUI's Node.js context

Closes#31182
Supersedes #31185

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Related PR Found

PR #31185: fix(tui): enable client-side filtering for session search dialogs
#31185

Relationship: According to the current PR description, #31185 is a "superseded skipFilter workaround" that is being replaced by this approach. The current PR (31199) takes a different solution path by replacing @solid-primitives/scheduled with manual debounce instead of using a skipFilter workaround.

Both PRs address the same issue (#31182) where session search filtering is broken due to the Node.js compatibility problem introduced by the build condition changes in PR #30873.

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