fix(desktop): normalize Windows inbox filing paths

[h4yfans]

What

Fix Windows inbox folder filing by normalizing vault-relative paths and the inline folder-create flow.

Why

A Windows user reported in #136 that creating a folder while filing a note/link could leave the app unresponsive, and after restart the folder existed but the item still remained in Inbox. The filing flow was mixing Windows \\-delimited relative paths with /-delimited folder ids.

How

• add normalizeRelativePath and use it anywhere the desktop app emits vault-relative note, folder, watcher, inbox, or attachment paths
• normalize folder search and AI suggestion paths in the inbox filing UI
• update inline folder creation to insert the new folder into the React Query cache immediately instead of waiting for a refetch
• add and update cross-platform tests so normalized relative paths are asserted explicitly

Type

• fix — bug fix
• feat — new feature
• refactor — restructure without behavior change
• style — visual/UI only
• perf — performance improvement
• test — adding or updating tests
• chore — tooling, deps, config
• docs — documentation only
• ci — CI/CD changes

Test plan

• Unit tests added/updated
• Integration tests added/updated
• Manual testing (describe below)
• pnpm lint
• pnpm typecheck
• pnpm test
• pnpm ipc:check

Screenshots

• N/A (behavioral fix, no visible UI change)

Checklist

• Self-reviewed the diff
• No hardcoded secrets or credentials
• Files stay under ~500 LOC
• Follows immutable data patterns