feat(ui): responsive sweep round 2 + flatten updates tab

[pachev]

Closes #26. Closes #20.

What this does

Second-pass responsive sweep through the LiveView page code — picks up the spots that the round-1 component-library work in #25 didn't touch.

Adopt ui_table where raw <table> still lived

• Settings → SSH Keys (settings_live.ex): handcrafted <table class="table table-zebra"> → ui_table. The list is small so no pagination; delete button slots cleanly into an unlabeled right-aligned :col.
• Application detail → Top by memory / Top by message queue (application_live/view.ex): the proc_table private helper was a parallel raw-table implementation. Rewritten to delegate to ui_table with the title in the :action_bar slot. Both call sites pass an explicit id instead of deriving one from the title.

Add sm: breakpoint to page-level 4-stat grids

These were grid-cols-2 lg:grid-cols-4 with no sm: step, so labels wrapped awkwardly at 320–375px:

• dashboard_live.ex (fleet overview stats)
• server_live/overview_tab.ex (server detail stats)
• application_live/view.ex (app detail stats)

All three now grid-cols-1 sm:grid-cols-2 lg:grid-cols-4.

Stack-on-xs fixes for grids with no fallback

• dashboard_live.ex Add Server modal SSH user / Port inputs: grid-cols-2 → grid-cols-1 sm:grid-cols-2
• application_live/view.ex memory-breakdown legend: same fix

Adopt ui_kv_table for server settings Connection

server_live/settings_tab.ex: the Connection block was a <dl class="grid grid-cols-2"> inside a ui_card. Replaced with ui_kv_table, which already stacks flex-col sm:flex-row on xs. The "SSH details for this host" subtitle is dropped — consistent with how the Application Info kv_table is used; the title "Connection" inside the Settings tab already provides context.

Anti-patterns we already fixed in ui_*

Two pre-existing instances in page code of patterns that #25 rewrote in the shared components:

• System snapshot header (application_live/view.ex:106): <header class="flex items-center"> + <span class="flex-1" /> spacer + badge → wrapping flex row with ml-auto on the badge. Same fix as ui_card_title.
• snapshot_row (application_live/view.ex:155): w-44 shrink-0 label column → flex-col sm:flex-row stacking. Same fix as ui_kv_table.

Flatten Updates tab to match pen design

Not in the original issue checklist but caught during visual review:

server_live/updates_tab.ex wrapped its ui_table inside a ui_card padded={false}, producing a card-inside-a-card with no breathing room on the right edge. Pen frame PFTPt shows the Updates section as a page-level header (title + scan status + badge) above a single bare table card — same shape as the Releases tab. Refactored to match. Empty states stay wrapped in ui_card so ui_empty keeps its frame.

Design-check protocol

Per the issue comment: every change here is either a responsive-breakpoint addition or adoption of a component that already exists in components.pen. No new components introduced, no substantial visual reshapes that needed a pen update first.

Filed #29 for a future ui_table mobile variant (card-stack vs scroll vs priority) — that one IS a new layout primitive and is explicitly blocked on a pen update before any code.

Verification

• mix precommit clean: compile --warnings-as-errors, deps.unlock --unused, format, credo --strict (no issues), mix test (277 tests, 0 failures)
• Visual verification with preview_screenshot at 375px viewport: Dashboard, Settings (SSH Keys), Server Settings (Connection), Server Overview, Updates tab, and App detail (snapshot + proc tables). Confirmed at desktop 1280px too for the Updates tab refactor.

Done-when checklist (from issue body)

• Every checkbox in the issue is either addressed or consciously dismissed
• No new horizontal-scroll surprises at 375 / 768 / 1024 viewports
• mix precommit clean