Tool-call icons rendered inconsistently across MCP servers: Linear and Notion came out as flat silhouettes, GitHub washed out near-white in dark mode, and Notion's block logo collapsed into a featureless square. Root cause was two CSS filter systems fighting on the same <img>, with the winner decided per-URL.

What this PR does

1. Bundles the three brand SVGs directly named in the bug: notion.svg, linear.svg, figma-black.svg (monochrome-safe variant), and figma-color.svg (full-colour reference variant). All normalised to the repo's 256x256 viewBox, registered in icons.json so they appear in the icon picker, and mapped to the existing monochrome mode in defaultParametersForBuiltinIcons.

2. Adds site/src/pages/AgentsPage/data/knownMcpServers.ts, a small registry keyed on Server URL hostname patterns. The MCP server admin form watches the URL field and pre-fills any empty sibling fields (display name, slug, icon URL) when a known host is recognised. User input is never overwritten. When the icon URL is pre-filled, the form auto-expands the Details section so the suggested icon is visible before save. Clearing the icon field while a known URL is present re-suggests the bundled default so admins do not have to retype the URL to recover the suggestion.

   Registry starts with the brands this PR bundles (Notion, Linear, Figma) plus the popular brands we already shipped (GitHub, GitLab, Bitbucket, Slack, Discord). Additional brands land in the follow-up PR below.

3. Drops the class-based silhouette filter and the Notion regex special case from ToolIcon. External MCP icons now route through the single ExternalImage + getExternalImageStylesFromUrl pipeline:

   • Bundled /icon/*.svg paths receive the theme-aware monochrome filter (grayscale(100%) contrast(0%) brightness(70%) in light, brightness(250%) in dark), producing a uniform muted silhouette that matches the surrounding lucide icons.
   • Cross-origin URLs not in the bundled map fall through unfiltered, matching the MCP server pill rendering.
   • There is no longer any code path where two filter systems fight on the same <img>.

Follow-up PR

A data-only follow-up will land the remaining 12 popular MCP brand bundles I had ready (Atlassian, Auth0, Cloudflare, Databricks, Datadog, Firecrawl, Grafana Labs, MongoDB, Netlify, PagerDuty, Sentry, Snowflake) plus their icons.json / externalImages.ts / knownMcpServers.ts entries. Keeping them out of this PR holds the surface area tight while the platform pieces (filter pipeline collapse, form prefill, clear-restore) get reviewed.

Migration

Existing MCP server entries whose icon_url was set by an administrator to a third-party CDN URL keep working: they render unfiltered through ExternalImage, the same way the MCP server pill renders them today. They'll start using the bundled icons when an administrator re-saves the server, either by accepting the URL-prefill suggestion or by selecting the bundled icon from the picker. No backend migration is required.

Testing

• MCPToolNotionIconBundled story in Tool.stories.tsx exercises the bundled-icon path and asserts the inline monochrome filter is applied.
• MCPToolNotionIcon story keeps regression coverage for the cross-origin Brandfetch URL.
• CreateServerKnownUrlPrefill, CreateServerKnownUrlPrefillRespectsExistingValues, and CreateServerKnownUrlIconRestoresOnClear stories in MCPServerAdminPanel.stories.tsx exercise the URL-host-keyed prefill and the clear-restore behaviour on both empty and partially-filled forms.
• Existing tool-rendering stories updated to drop assertions on the removed wrapper container and silhouette filter classes.
• All affected story tests pass locally: Tool.stories.tsx (115/115), MCPServerAdminPanel.stories.tsx (19/19).

_{This PR was generated by Coder Agents.}