Fix dropdown closing after input blur

[ScribleSean]

Fixes #136.

Opening results marked the list as being interacted with before a user had touched it. The input blur handler then ignored focus changes and left the dropdown visible after users moved focus away.

Keep the interaction flag false when opening results. The existing list mousedown handler still preserves option selection.

Validation:

• All 56 Chromium browser tests pass on current main plus this patch, including regular and Popover focus-away, click-away and selection regressions.
• TypeScript compilation, bundling and custom-elements manifest generation pass.
• The stock lint/prebuild step currently crashes with escompat/no-optional-chaining: this.findConfigFile is not a function. The same crash occurs when linting unchanged src/debounce.ts; no tooling changes are included here. Lint and build passed on the originally tested September 22 dependency lockfile.

AI assistance: Codex (GPT-6 family; exact preparation variant was not exposed) assisted with investigation, implementation and validation. I reviewed and approved all work before submission and remain responsible for this contribution.

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Copilot review overview

🟢 Approval recommended

The focused fix preserves selection handling, includes regression coverage, and has no unresolved findings.

Review effort: Balanced
Findings: None