Make /api public and fix landing page pill icon/text visibility

[Copilot]

/api was gated behind auth, breaking links from the index and docs pages. Landing page pills also had broken icon/text rendering: active state made icons invisible (black icon on black background), and the API & MCP section was missing icons entirely.

Changes

• main.go: Set "/api": false — API docs are public reference material
• home/home.go: Add .preview-tab.active img { filter:brightness(0) invert(1); } so icons invert to white on active (black) pill background
• home/home.go: Add icons to API & MCP section pills, matching the "What's Available" pill style

/* Before: icon invisible when tab active */
.preview-tab.active { background:#000; color:#fff; border-color:#000; }

/* After: icon inverts to white on active tab */
.preview-tab.active { background:#000; color:#fff; border-color:#000; }
.preview-tab.active img { filter:brightness(0) invert(1); }

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