Add collapsible primary UI sections (ticket 035)

Log viewer (FilterBar+LogTimeline+LogPreview), Params, Metrics, and
Dashboards can each be collapsed/expanded via a toggle next to their
existing help icon. Collapsed state persists per-section in
localStorage (ottyl.collapsedSections) and content is hidden with the
`hidden` attribute rather than unmounted, so in-progress form state
(a half-filled Metrics/Params form, in-progress Dashboards panel
edits) survives a collapse/expand cycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

tickets/035-collapsible-sections.md

@@ -1,34 +0,0 @@
-# 035 — Collapsible primary UI sections
-
-## Summary
-
-`App.tsx` stacks the Log viewer (`LogTimeline` + `LogPreview`), Params
-([034](034-params-declaration-ui.md)), `Metrics`, and `Dashboards` vertically
-with no way to collapse any of them. On a small screen — or just when only
-one section is being worked on — the others take up space and force
-scrolling. Make each section collapsible.
-
-## Scope
-
-- Each of the four sections (Log viewer, Params, Metrics, Dashboards) gets a
-  collapse/expand toggle in its header, next to its existing "?" help icon.
-- Collapsed state persists across reloads per-section, via `localStorage`
-  (same pattern as `LogPreview`'s `VISIBLE_PARAM_COLUMNS_STORAGE_KEY` at
-  `webapp/src/components/LogPreview.tsx:13`).
-- A collapsed section still shows its header (title + toggle), just not its
-  body/content.
-- Collapsing a section must not tear down state that would be lost/reset on
-  re-expand (e.g. `Dashboards`' in-progress panel edits, `Metrics`' declare
-  form) — hide with CSS/conditional render at the container level, not by
-  unmounting stateful subtrees.
-
-## Acceptance criteria
-
-- Each section can be independently collapsed and re-expanded.
-- Reloading the page preserves each section's collapsed/expanded state.
-- Collapsing a section with unsaved in-progress input (e.g. a half-filled
-  Metrics declare form) and re-expanding it preserves that input.
-
-## Depends on
-
-- [034 — Params declaration UI](034-params-declaration-ui.md)