feat(desktop): typed ref hovers, field completion and shape refresh

[gandarfh]

What

Desktop integration for typed {{alias.path}} resolution served by the language server:

• save_block_result (command + wrapper) now carries the block's alias, so successful runs land an inferred response shape; both block panels send the custom httui/refresh notification after an aliased save so the server republishes field diagnostics.
• Read-side {{alias…}} cache resolution now looks up the latest result by (file_path, alias) — the write side keys HTTP rows by a request+env hash the document scanner cannot reproduce, so the old content-hash lookup missed every row (hover always claimed the block had never run).
• httui-core bumped to pick up the WAL journal mode and the response shape cache.
• DB panel split into sibling hooks (explain, paging, cache hydrate, legacy migration) to clear the size gate; panel + hooks covered by new tests (48 checks in the db fenced suite).

Validation

Manually verified in the app: hover shows the field type from the last run, {{alias.response. completes with real fields, and a field typo gets a warning squiggle with a suggestion. Full unit suite (3207), clippy and prettier green.