polish(security): group meta-row actions + let the page fill width

[graydawnc]

What

Two small alignment fixes on the Security page:

1. Meta-row actions grouped right. The Rescan ↻ button moves to the right edge next to the Ignored entry, and the Ignored entry loses its "Ignored" text label — both are now icon-only with tooltips, forming a uniform action cluster on the right. The stats span's flex-1 pushes the cluster over.
2. Page fills width. Drops the max-w-[720px] cap on the meta row + findings list so Security fills the content width like every other main surface (Shares / Projects / Library), removing the empty right gutter when the sidebar is collapsed.

Why

• The meta row had two visually different action affordances (an icon-only ↻ on the left paired with the timestamp, and a text+icon "Ignored" pill on the right). Grouping both as icon-only on the right reads as one consistent control set.
• Security was the only main page constrained to 720px; siblings fill the width, so a collapsed sidebar left an unintentional-looking gap. Long finding values / session titles also get more room before truncating.

How it connects

• SecurityPage.tsx: removes the left-group wrapper (rescan now a sibling in a right-aligned flex gap-1 cluster), makes the Ignored button icon-only (w-5 h-5, keeps title + aria-label), and removes the two max-w-[720px] caps (meta row + scroll content). The scanner-unavailable card and empty-state copy keep their own readable caps.
• Supersedes the rescan-adjacent-to-timestamp layout from fix(security): keep rescan icon glued to the scanned-time stamp #327 — the timestamp↔refresh adjacency is replaced by the grouped-right cluster.

Test plan

• security-scan-meta-stability: drops the now-moot rescan↔timestamp adjacency assertion; keeps the during-scan "rescan button doesn't shift" assertion (still holds — it's right-anchored).
• security-ignored-entry: asserts the icon button's aria-label (was: visible "Ignored" text).
• security-blast-radius green — full-width didn't disturb the finding rows.
• app typecheck clean.

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