Add additional missing icons sourced from Phosphor for the lightspeed collection

[brandonmarshal]

Summary

Adds 8 icons still missing from the lightspeed icon collection, found while cross-checking a set of design mockups against the existing assets/icons/lightspeed/ set. Each icon below was confirmed absent (or confirmed as a shape mismatch against an existing icon) before being sourced.

New icons

• circle.svg — plain outline circle (radio-style indicator glyph)
• coins.svg — stacked coin glyph; distinct from the existing stack.svg (a layered-squares glyph), which doesn't match a coin-stack shape
• hard-drives.svg — stacked server/hard-drive rack glyph; distinct from the existing database.svg (a cylinder/drum glyph)
• chart-bar.svg — ascending vertical bar chart; distinct from the existing chart-line-up.svg/trending-up.svg (diagonal line charts)
• users-three.svg — three-person group glyph, for contexts needing a team/group icon distinct from the existing two-person users.svg
• paper-plane-tilt.svg — tilted paper-plane/send glyph
• git-fork.svg — single node branching into two, for phase/roadmap-style UI
• chat-circle-dots.svg — circular chat bubble with a three-dot ellipsis; distinct from the existing chat.svg (a plain bubble silhouette, no dots)

All 8 are sourced from phosphor-icons/core's assets/regular set and verified byte-for-byte against the upstream Phosphor path data. Each file follows this collection's existing convention: viewBox="0 0 256 256", fill="currentColor" on <path> (not the <svg> root), matching assets/icons/lightspeed/README.md.

No PHP changes — LS_Plugin\Icons auto-registers every .svg dropped into assets/icons/lightspeed/ on init.

Scope and exclusions

This PR only adds the 8 SVG files above. It does not wire any icon into a theme template, pattern, or block instance — that consumption work is expected in a follow-up (ls-theme or similar), matching how prior icon-sourcing PRs (#21, #24) in this repo were scoped.

Test plan

• npm run plugin:validate — passes
• npm run security:scan — no new issues introduced by this branch (2 pre-existing warnings in taxonomy-filter/render.php, unrelated to this change)
• xmllint --noout on all 8 new SVG files — valid XML
• Each new SVG's <path d="..."> verified byte-for-byte against Phosphor's assets/regular source
• Confirm all 8 new icons appear correctly in the block editor's icon picker on WordPress 7.1+

[brandonmarshal]

Linear agent review completed — no actionable changes required. The PR is approved.